Fixes issues, adopts native browser player by default

[EddyLB]

• Adopts native browser player by default
• Adds translations and fixes typos
• Fixes Video Js Warnings #133, Sync Error #205: crash occurring when ExifTool returns a wrong date_creation (thanks to @Catfriend1)
• Fixes player v7 not working [bootstrap_default theme] #136: updates VideoJS player to version 7.21.5 (thanks to @klaoun)
• Fixes Unsupported operand types #179, Wrong Datatype for "Duration" for particular files #197, Sync Error #205: a crash occurring when the duration returned by ExifTool is an array
• Fixes Sync Error #205: deprecated float to int casting (thanks to @klaoun)
• Fixes Too short videos cause unrecoverable error #140, sync breaks on short videos #214: no thumbnail produced from very short videos
• Fixes Can not reach synchronization tab #192, Fatal error on Synchronize panel and Warning error on Configuration panel #216: calls binaries with system() or exec() according to their availability
• Fixes Installation from webUI incompatible with piwigo 13.3 #194, No video posters #201, Installation of VideoJS Plugin with Piwigo #203, Warning: Undefined array key "resolution" #217, Error displayed in settings #228: undefined array key "resolution" warning (thanks to @klaoun)
• Fixes SMime type unknown #145, Windows: Undefined index: vjs_sync in C:\piwigo\plugins\piwigo-videojs\admin\admin_sync.php on line 78 #153, Thumbnails won't generate #162, admin_sync php fatal error #189, Fatal error when trying to "Synchronise" from the plugin administration page #204, Error on Synchronization of metadata information and poster creation #222: undefined array key "vjs_sync" warning