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 lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
s2s_whitelist = {
    "example.org",
}
```