globalC -> globalF
New notation: iPropG, iFunctorG

Introduce the notion of "Frame Shift Assertions", and use to prove the rules about inv and auth at once for pvs and wp

Yeah, the name is horrible... but on the plus side, I think it should be possible to show that atomic triples and atomic shifts are also frame shift assertions, and then we get all this stuff for them for free.

Instead, I separate it into a total function and a predicate
describe whether the action is allowed or not. This has some
advantages:

* It is much easier to deal with total functions and predicates
  in Coq than with functions into option.
* Already existing functions do not need to be wrapped. Instead,
  when using a local update you end up with a sensible side
  condition as a Coq Prop.
* The definition of local updates (and all CMRA instances) no
  longer depend on option.