Refactor the Dwoo_Template_Mahara files

Bug 1231755

- Cleanup, documentation, and removing replicated code.

- Not checking for whether the file exists. We'll just make a list
of search paths and pass those through to Dwoo_Template_File, and
let it determine which path has the file.

- Eliminating the separate Dwoo_Template_Mahara classes for plugintypes,
and moving the custom logic for how plugintypes find their template files,
into the Plugin class itself.

Change-Id: I877a4221323333e8e8b6c6df54062a0f8bf2b817
Merge "Refactor the Dwoo_Template_Mahara files"