Add simplify pass for typical "archiving" filters

[mbrt]

Filters of the form:

{A B C D} -{E F G H}

Could be used as a catch all archive rule (e.g. either of these mail lists but not directed to me, or with this subject line).

This filter can become pretty big and so ignored by Gmail. Rewriting it into a set of filters like this:

A -{E F G H}
B -{E F G H}
...

Would solve the issue (if the exclusion list is short enough).

We should automatically apply this transformation in the SimplifyCriteria step.