- Removed unnecessary function in PreviewTapes
* Refactored, removed Sample::addToComposition

It was an extra, unnecessary step.
* Changed TapeComposition add/remove source

addSource and deleteSource have been refactored to take SampleInstance
instead.
* Cleaned up the messy gnl section

Refactored to be less messy in general. Tied up loose ends, etc after
finishing this feature.
+ Sample start and end is now saved
* Fixed the timeline being unordered
+ Added a Doxygen file
+ Added .gitattributes for line endings