Refactor/pdf creation

Moved logic from ViewAlbum controller to ImageAlbumService and made PdfDocument implement ImageAlbumDocument to abstract the document process and increase flexibility.

Good job. Please resolve the conflicts and feel free to merge afterwards.

added 13 commits

• e07d73a8...88940cbf - 8 commits from branch dev
• ae11bae2 - Move methods for creating pdf to a location to ImageAlbumService
• 75f23d3d - Add ImageAlbumDocument and implemented it in PdfDocument
• c2ba2152 - Rename album_pdf identifiers to album_document
• 47aa403d - Add javadoc to ImageAlbum.getDocument
• eeacef9d - Add javadoc to ImageAlbumDocument

Compare with previous version

merged

mentioned in commit 84c75015