Mk period in knesset should be closed with one method encapsulating all changes

[alonisser]

We need a method (on model perhaps?) to "close" mk period when he finishes in knesset
Currenly mk has "is_current" and :"end_date"
Various automatic schemes toggle either of them (mostly is_current) but don't change the other, causing all sorts of problems
We need a method to be called to properly "close" a member (Perhaps also "reopen")

1. Admin should be able to use this method to proper close from admin screen