Audit fixes

Fixing #58 and #59 (#60)

* Disable balancer trading during pool entry/exit

* Add test for modifier

* Only able to poke weights once after finished

* Cancel weight adjustment when removing token

* Cancel weight adjustment when adding token

* Refactor current tests

* Cancel weight adjustment for bind/unbind/rebind

* Testing if weight adjustment still works after revert

* Cancel weight adjustment when calling updateWeight