Move addin templates to a separate folder in the project.

This is both a tidy up of the solution and preparation for more
templates in the near future.
Merge pull request #439 from 7sharp9/master

Move addin templates to a separate folder in the project.
Fix invalid DIR parameter passed to `read-file-name'

The filename of the current buffer (instead of the dirname) was passed
as DIR parameter), resulting in an invalid directory where emacs starts
completion.

Also ensure that the project file exists.
Merge pull request #441 from juergenhoetzel/master

Fix invalid DIR parameter passed to `read-file-name'
Merge pull request #442 from fsharp/master

merge updates from master