Improve debug config selection in Flask/Django

[karthiknadig]

When we reach this part, while setting up django or flask:

Currently we show manage.py. even if that file does not exist. This is fine, in addition we should show files in the works space that are potential start up files. These should be listed in the order of most likely to least likely.

The point here is to avoid users having to type in the file if it is slightly different from app.py like say webapp.py