PHP 8.3 (part of Ubuntu 24.04) outputs a deprecated warning for properties that
were not in the class definition. Error below. There were a few of these
missing from the `Ebook`, `GitCommit`, `CollectionMembership`, `EbookSource`,
and `Contributor` classes. Adding them doesn't change any functionality, but it
does make it clearer what properties a class has.
Some of these properties are never set for `Ebook` instances created from the
filesystem, i.e., `Created` and `Updated`, and some of them need to be manually
set to make `Ebook` instances from the filesystem and the database match, e.g.,
`GitCommitId`, `CollectionEbookId`, `EbookSourceId`, and `ContributorId`.
Making the `Ebook` instances from the filesystem and the database match each
other makes it easier to spot bugs in the future.
Previous errors with PHP 8.3:
```
PHP Deprecated: Creation of dynamic property Ebook::$Created is deprecated in /standardebooks.org/web/lib/Traits/Accessor.php on line 42
PHP Deprecated: Creation of dynamic property Ebook::$Updated is deprecated in /standardebooks.org/web/lib/Traits/Accessor.php on line 42
PHP Deprecated: Creation of dynamic property GitCommit::$GitCommitId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$GitCommitId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$GitCommitId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$GitCommitId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$GitCommitId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property GitCommit::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property CollectionMembership::$CollectionEbookId is deprecated in /standardebooks.org/web/lib/Traits/Accessor.php on line 42
PHP Deprecated: Creation of dynamic property CollectionMembership::$EbookId is deprecated in /standardebooks.org/web/lib/Traits/Accessor.php on line 42
PHP Deprecated: Creation of dynamic property CollectionMembership::$CollectionId is deprecated in /standardebooks.org/web/lib/Traits/Accessor.php on line 42
PHP Deprecated: Creation of dynamic property EbookSource::$EbookSourceId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property EbookSource::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property EbookSource::$EbookSourceId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property EbookSource::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property Contributor::$ContributorId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property Contributor::$EbookId is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
PHP Deprecated: Creation of dynamic property Contributor::$SortOrder is deprecated in /standardebooks.org/web/lib/DbConnection.php on line 286
```
Also added `GetFoo()` methods for all the derived properties like `GetUrl()`, `GetHasDownloads()`, etc. Removed that logic from the constructor so that it's reusable in `Ebook::FromFilesystem()` and `Ebook::GetByIdentifier()`
