Remove primary key EbookSourceId

There is a one to many relationship between `Ebook` and `EbookSource`, and we
don't query by `EbookSourceId`. We add a `SortOrder` column to keep the sources
in the same order as specified in `content.opf`.

lib/Ebook.php

@@ -193,7 +193,7 @@ class Ebook{
 						SELECT *
 						from EbookSources
 						where EbookId = ?
-						order by EbookSourceId
+						order by SortOrder asc
 					', [$this->EbookId], EbookSource::class);
 		}
 
@@ -1790,8 +1790,9 @@ class Ebook{
 	 * @throws Exceptions\ValidationException
 	 */
 	private function AddSources(): void{
-		foreach($this->Sources as $source){
+		foreach($this->Sources as $sortOrder => $source){
 			$source->EbookId = $this->EbookId;
+			$source->SortOrder = $sortOrder;
 			$source->Create();
 		}
 	}

lib/EbookSource.php

@@ -3,10 +3,10 @@
 use Safe\DateTimeImmutable;
 
 class EbookSource{
-	public ?int $EbookSourceId = null;
 	public ?int $EbookId = null;
 	public EbookSourceType $Type;
 	public string $Url;
+	public ?int $SortOrder = null;
 
 	public static function FromTypeAndUrl(EbookSourceType $type, string $url): EbookSource{
 		$instance = new EbookSource();
@@ -39,6 +39,10 @@ class EbookSource{
 			$error->Add(new Exceptions\EbookSourceUrlRequiredException());
 		}
 
+		if(!isset($this->SortOrder)){
+			$error->Add(new Exceptions\EbookSourceSortOrderRequiredException());
+		}
+
 		if($error->HasExceptions){
 			throw $error;
 		}
@@ -50,12 +54,11 @@ class EbookSource{
 	public function Create(): void{
 		$this->Validate();
 		Db::Query('
-			INSERT into EbookSources (EbookId, Type, Url)
+			INSERT into EbookSources (EbookId, Type, Url, SortOrder)
 			values (?,
+				?,
 				?,
 				?)
-		', [$this->EbookId, $this->Type, $this->Url]);
-
-		$this->EbookSourceId = Db::GetLastInsertedId();
+		', [$this->EbookId, $this->Type, $this->Url, $this->SortOrder]);
 	}
 }

lib/Exceptions/EbookSourceSortOrderRequiredException.php

@@ -0,0 +1,7 @@
+<?
+namespace Exceptions;
+
+class EbookSourceSortOrderRequiredException extends AppException{
+	/** @var string $message */
+	protected $message = 'EbookSource SortOrder required.';
+}