Highscore improvements

[LewisGaul]

Meta issue bringing together the planned highscore improvements.

Bugs

• Moving the highscores window with a filter menu open doesn't move the filter menu #72 Moving the highscores window with a filter menu open doesn't move the filter menu
• Highlighted highscore row using smaller font #84 Highlighted highscore row using smaller font on Windows
• Highscores window sizing issue #96 Highscores window sizing issue

High priority

• Add option for merging local highscores  #80 Add option for fetching highscores
• Local highscores view very slow with lots of entries #82 Local highscores view very slow with lots of entries
• Save highscores to file with mouse tracking info #40 Save highscores to file with mouse tracking info [in progress]
• Store failed highscore uploads and retry later  #79 Store failed highscore uploads and retry later
• Validate highscores being posted to remote DB #63 Validate highscores being posted to remote DB
• Solve issue of highscore name uniqueness #91 Solve issue of highscore name uniqueness

Enhancements

• Show settings corresponding to displayed highscores in highscore window #85 Show settings corresponding to displayed highscores in highscore window
• Update displayed highscores when a new one is set #86 Update displayed highscores when a new one is set
• Add compatibility layer for legacy highscores #87 Add compatibility layer for legacy highscores
• Handle opening highscores window when a custom difficulty is in play #88 Handle opening highscores window when a custom difficulty is in play
• Highscores module tidyup/tests #89 Add test coverage of highscores module [mostly complete]