Database version downgrade from 7 to Version 6.

This commit will downgrade the database version from 7 to 6.
The newest app on the playstore is using version 5.

Note: I removed the Profile/friend table upgrade because this hasn't been pushed to the devices of our users.
So we only need to create the table.
Merge pull request #97 from ratan12/Database_downgrade

Database version downgrade from 7 to Version 6.