Multiplayer: Add missing utilities to lobby screen

[percyqaz]

Song sync

Practice mode should be quickly accessible from lobby to let users sync the chart/test the sync before playing

Perhaps a cap could be in place that you can only play the first 200 notes in multiplayer to not 'spoil' the chart

Mods

Mods button should allow host to select mods from within the lobby

Support should be added for user-specific mods which will be a pain to deal with