Update capability checks on user profile

Added a filter to the capability check on /includes/profile.php. Default
capability is 'manage_options' (administrator).
Fix spelling mistake on user profile capability
Update filter name on profile capability

Changed to 'pmpro_edit_member_capability'
Merge pull request #54 from scottsousa/dev

Add pmpro_edit_member_capability filter so you can override capability needed to see the change membership level field on the edit profile page.