Plugin updates for v2.2

All plugins as well as the Essence theme are now fully compatible with PHP Melody v2.2.1.

All changes:

Advanced Newsletters v2.1
- Improved compatibility with https sites
- Fixed the confirmation of deleting newsletters

Progress Thumbnails v1.1
- Fixed thumbnail generation for long videos that would create a too big image
- Compatibility changes with FFmpeg Thumbnail generator v1.4

YouTube Downloader v1.1
- Important fixes to download engine due to YouTube changes
- Prevention of double downloads with long videos

FFmpeg Thumbnail generator v1.4
- Improved compatibility with videos in custom directories
- Fixed compatibility with custom admin directories in 2.2

YouTube Autoimport v1.5
- Minor v2.2 compatibility fixes
- Fixed the confirmation of deleting sources

Essence Theme v2.2.1
- Documentation updates
- Moved players to separate directory
- v2.2 updates and playlists support
- Index page style fixes for loading slider (images no longer show up below each other when the page is loading) and article listing