Move all source files into src directory.

Preparing for adding unit tests and data.
Capitalize cabal file. (gramophone.cabal -> Gramophone.cabal)
Remove old GTK file.

Left over from before the switch to Yesod-based GUI.
Move a misplaced module

Moved Gramophone/Database/Monad.hs to
Gramophone/Core/Database/Monad.hs. This must have been missed when
the Database module was moved into Core.
WIP: Adding tests.
Start to add tests for database

Currently just creates and deletes a temporary database file.