Refactor libraries

[DannyBen]

Refactor libraries in preparation to allow adding external libraries.

This PR adds a LibrarySource class, and moves all library files to the new internal library source at lib/bashly/libraries.

Additional changes needed:

• The bashly add command should be changed to a more generic form
• Library args should probably be removed - which means bashly add comp function will need to be renamed to bashly add comp-function.
• The bashly generate --upgrade functionality should consider external source
• The bashly add command should allow external folders / git

cc #333