Tiny changes
Added CaseInsensitive flag into the custom tilesets search
Music and sound playback completely moved into own class
Note: When you built editor with SDL which built with LibMAD library
(if you built editor without libmad, MP3 will be played via QMediaPlayer),
be careful with testing of sounds: play of the MP3 sound will stop
music playback and you need to restart music playback after.
But, if soundpack using other formats (WAV, OGG, etc), will be played
normally without any problems.