[WIP] New mods repository

[ArseniyShestakov]

More information on repository is available on wiki:
https://wiki.vcmi.eu/Mods_repository

Changes:

• Mods game started with now serialized inside StartInfo. So list of mods available in save file header.
• New "Show mods" button for loading screen. Text changes to orange "Mods error!" when some mods missing or have different version.
• Player will also get warning on attempt to start game while mods check did not pass.

TODO:

• Lib and Launcher: store commit hash for mods in addition to version.
• Client: implement VLC reload when gameplay is finished.
• Launcher: Implement command-line interface for mod management.
• Client: feature to run launcher in background to get missing mods and then reload VLC.
• Launcher: Implement redirection support for Qt 5.5 and older.
• Mods repository: implement checking of repository.json against schema on Travis.

IDEAS:

• Another nice advantage of git. Any mod might have own "repository.json" inside repo so player will be able to add this single mod to his launcher even if mod not included in main VCMI repository, or if only older version is included.

[nullkiller]

I expect this work is no longer actual