mod_http_oauth2: Refactor to return all errors to Device clients Previously only a single case was returned to device clients, now all error conditions that pass trough the error_response() are covered.

This module blocks configured queries that change server state.

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

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