Simple Submit Rules plugin

Gerrit plugin to provide simple submit rules and a rest API to configure them.

By simple, we mean any rule that can be described in one sentence. Or fits in a tweet.

Having a set of simple rules makes composition easier, thus allowing harder rules to be defined ... in a simple way :)

Of course, this plugin can't contain all the simple rules one can think of, and will only contain rules that seem popular or interesting to have.