Added the verified column in the administrator table.

This column will be changed to true once the administrator is approved
Added the rails_admin gem
After the installation of the rails_admin gem
Added the database migration for the verification string and the verification 
boolean.
Show on the administrator page if the administrator is verified or not.
The verification function in the controller.

Routes.rb has been configured already
The verification form that is shown to the user and then verified.

* The administrator registers
* One of the present administrators, goes into the database and changes the verification
string for the new administrator and sends an email to the new administrator
containing the verification string to be entered.

On the edit profile page a link to the verify_administrator is shown, if the administrator
has not yet been verified.

The manual step of mailing can't be avoided, because, since only some people are allowed
to be verified admins, it's important to put a manual check.
Added the verified and unverified tags in the navbar.
Added appropriate text in the verify view.
Merge branch 'administrator-verfication'

Introduced the concept of Verified and Unverified administrator.

When the administrator signs up, the verification string will be initialised with some value.

THe verified boolean for this new record in the database will be false.

After this, once the administrator identity is verified, the verification string will be changed in the database and
an email will be sent to the new administrator, giving him/her the verification string, which can
be entered in the administrator#verify action. Thus, verifying him/her.