Update Substrate to rc4 (#175)

* Bump Substrate to rc4

* Add BaseCallFilter type

* Add DenyUnsafe to SystemApi extension

* Use new ServiceBuilder build functions

* Add BaseCallFilter to test runtimes

* Remove old comments

* Add `rev` and `git` fields back

Turns out that if you don't have these future release candidates will
be used if available. For instance, once `rc5` is released a fresh pull
would use that instead of `rc4` which is what we want.

* Use tag release instead of specific commit

Will make scripted updates easier in the future

* Add short script to update between `rc` versions

* Update scripts/update_rc.sh

Co-authored-by: Tomasz Drwięga <[email protected]>