Introduce kick method on P-Rep delegation

[redlarva]

Even though the user's veOMM balance will linearly decay to 0 and will be 0 after the expiration of the locking period, its voting weight will not be changed until and unless the user interacts with OMM application.

• lock/unlock OMM
• Change delegation manually

However, once the locking period expires, anyone can “kick” the user by creating a checkpoint for that user and, essentially, resetting the user to no boost.