Add Soundscape API. Add Source Installation Assignments. Add Soundscape Group Creation to GUI.

[mitchmindtree]

Refactor soundscape thread with a clearer Soundscape API.

This gives a clearer API for interactions with the soundscape thread from the rest of the codebase (rather than just passing around a raw channel).

Allow for assigning installations to sources. Add ticks to soundscape.

Also ensures that spread or radians adjustments via the GUI causes the sounds with the associated source to update in realtime.

Track speaker positions and installations on the soundscape thread.

Add a field to the soundscape for tracking active sounds.

Implement pause and play methods for Sound and Soundscape.

Add soundscape::movement module with BoundingBox for speaker areas.

Installation areas are calculated by producing a BoundingBox around all speakers that exist within the installation. This will be used to constrain the path of travel for soundscape sounds moving throughout the exhibition.

Begin implementing soundscape groups.

Add s SoundscapeEditor GUI panel, allowing for add/removing Groups.

This adds the ability to add and remove soundscape groups. The next step is to add sets of per-group constraints controlled via the GUI. These include:

• Toggle-able sliders for min and max occurence rate, with readable rates like "2 times per second, "3 times per minute". Headed with a "Occurrence Rate" Text.
• Toggle-able Sliders for controlling the min/max number of sounds that may be played back at once.
• A multi-select list for choosing applicable effects.

Related to #55.