History-version-file creation/updataion modified and implemented GApps toolbar

* History-version-file creation/updataion modified

1) Version-file is now on gets created implicitly whenever you create a new document or update a document.
2) Important point to note here is that whether you insert/update only use "save()" function to do so.

* GApps toolbar Implementaion

1) In file (settings.py), created a list named "GAPPS" that stores names of GApps which has been discussed earlier.
2) In file (ndf_tags.py), created an inclusion tag named "get_gapps_toolbar()", which returns a template named "gapps_toolbar.html".
3) To implement this toolbar, some of the views and templates restructured accordingly.

* Urls modified