mod_unified_push: Remove dependency on trunk util.jwt (0.12 compat) This should allow the module to work on 0.12, while preserving expiry checking (which was not built in to 0.12's util.jwt).

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```