Improved solo high scores, basic band high scores (#883)

* WIP Implementation of better solo high scores.
Solo high scores are now displayed when there is exactly one non-bot player present.
High scores are now retrieved per player, song and instrument. Added a new cache for the above when retrieving high scores for the same player + instrument for many songs in a row.
Removed instrument icon for high scores on Music Library song list, replaced with a FC indicator sprite (using a placeholder sprite for now).
Moved retrieval of solo high scores per song to MusicLibraryMenu.
Marked several methods as Obsolete

* Reworked Player High Scores due to feedback. Player High Scores now keep track of the best percentage and best score (matches existing behaviour)
Added basic implementation for Band High Scores
Removed magic number in RecommandedSongs

* Update Band High Scores cache when a new Band High Score is set.
Fixed Best percentage scores not being loaded.
Fixed Best percentage score not being displayed if its different to the best score.

* Fixed bug when saving a band high score for the first time.
Fixed best percentage not loading when multiple profiles have played the same song+instrument combination.

* Added new difficulty icons, and display them in solo high scores.

* Removed obsolete method from ScoreContainer
Added comments for GetBestPercentageScore()

* Update YARG.Core

* Resolved issues from PR feedback

* Tweaked "Score not saved" message