Small improvements

Actually the snakefire bin is using system default python.

But user can install other pythons and make them default, what will cause problems.

1 .Change this to remove conflicts with other installed python version, fixing to call `python2.7`.

Other small improvements:

2. Rename .desktop to `snakefire.desktop`.

3. Change package format to 'quilt'.

4. Remove unused files under `resources`.