Add form and link in campaign block making enabling/disabling easier.

Both ajax modal form and no javascript is supported.
It prefers rule_page and similar, but falls back to rule_path if it isn't a node.
Add rough rules integration.

An event is fired when the campaign rules are changed.
Except when nodes are deleted, since that was deemed
unneccesary in my use-case.
Only show link to users that are allowed to use it.
Merge branch 'feature-rules' into merge