MAIN: Move ResourceTree to resourcetree.h/.cpp
MAIN: Move populateTree() to ResourceTree
MAIN: Move layout creation to createLayout()
SOUND: Add SoundManager::getChannelSamplesPlayed()

Returns the number of samples a channel has already played.
SOUND: Add SoundManager::getChannelDurationPlayed()

Return the time in milliseconds a channel has already played.
SOUND: Keep unqueueing buffers when the stream ended

Otherwise, the samples/time played will be off.
SOUND: Completely remove makeLoopingAudioStream()
SOUND: Oops, fix LoopingAudioStream::getLength()
SOUND: Oops, fix LoopingAudioStream::getDuration()
SOUND: Add LoopingAudioStream::getLengthOnce()

Return the length of one loop iteration.
SOUND: Add LoopingAudioStream::getDurationOnce()

Return the duration of one loop iteration.
SOUND: Add SoundManager::isPaused()
MAIN: Add ResourceTreeItem::getSoundDuration()
MAIN: Add SoundControls

Showing the sound playback position and total duration.