Song Select Categories

[aoki-marika]

Currently, songs can only be viewed in the way they are organized on the filesystem. This is alright for basic categorization such as using boxes to denote different sources, but falls apart when you want to instead say, group by difficulty level, without making changes to the filesystem.

I think that, like in GITADORA, you should be able to cycle between different grouping tabs (title, source, difficulty, etc.) within song select. In addition, songs should be independent of boxes, instead being changed to "collections" (more clear terminology) that form a many-to-many relationship with songs, which then also get their own grouping tab. This allows the additional feature of assigning songs to several collections, adding support for things like favourites.

I also propose that this should be accompanied by a database rewrite, using a more proper system such as plain SQLite or Microsoft's Entity Framework. The current system of serializing objects to disk is.. interesting, to say the least, but greatly inefficient, especially for these more complex tasks.

[limyz]

Do give the Config_ini_to_Sqlite branch a look, it was previously done by @fisyher, but yet to be merged