Made SpriteGroup frustum culling a protected field.
Fixed SpriteGroup rotation.
Added ability to load TileSheet using a properties file.
Added ability to get TileSheet strip index from ID.
Appended TileSheet functions that use ID to have "ById" at end for function names.
TileSheet's are now cached by their URL so if loaded by URL, they can be reloaded instead of recreated.
Added ability for Sprite to be loaded from a Properties file.
Separated sprite loading function so it can be used by SpriteGroup.
Fixed bug (seems more like "bad decision") where if a Tilesheet was created as opposed to loaded for Sprite and SpriteGroup, it would have an additional reference because they would add ref to the tilesheet when it already had one ref (from creation).
Added ability to load SpriteGroup via Properties file.
Fixed bug in SpriteGroup where if a child was set and then replaced by "default" or "transparent", it would still be referenced and wouldn't be freed.
Added ability to load Sprite and SpriteGroup's default tile using TileSheet strips and frames.
Added ability to load Sprites and SpriteGroups in a .scene.
Minor change to how SpriteGroup loads children (doesn't have a "url" namespace, instead looks for "path" property and uses that if it exists)
Merge branch 'next' of github.com:rcmaniac25/GamePlay into StaticCodeAnalysis