Add help text description to ``Application`` form.
Relocate user account navigation items.

The links can be found in the right context.
Add ``User`` account removal functionality.

https://github.com/madewithbytes/us_ignite/issues/58

When a user remove it’s account any every user generated
content in the site will be removed:

    - User profile.
    - Owned applications.

Any URL pointing to a removed resource will return an HTTP 404.
The operation is irreversible.

Closes #58.
Remove change password functinality to ``Mozilla Persona`` users.

The functionality is not available to them, since
the password of the account is managed in ``Mozilla Persona``