Add both non-expansive and contractive functors, and bundle them for the general Iris instance as well as the global functor construction

This allows us to move the \later in the user-defined functor to any place we want.
In particular, we can now have "\later (iProp -> iProp)" in the ghost CMRA.

Tactics like wp_proj should always solve all to_val side-conditions. The
tactic wp_done is used to handle these in a uniform way.

Since functor instances are just used as combinators, there is really
no need for functors that are not contractive.

make the global functor stuff in the various constructions more uniform; change it such that barrier/proof does not have to repeat the functors it needs

add a version of [cancel] that works with goals of the form [_ |- pvs _]; and use that for the barrier proof

write tactics to move particular assertions to the front, and to introduce a (*) while taking paticular assertions to the left/right

I talked with Christian, he is not the original author and forgot where it came
from, probably some coq-club mail.