Added new recursive minmax check for non-presence containers
This makes validation checks stricter, including check of incoming RPCs
Renamed xml_yang_check_list_unique_minmax() to xml_yang_minmax_recurse()
Fixed again: [YANG min-elements within non-presence container does not work](https://github.com/clicon/clixon/issues/355)
* Load/save JSON config file did not work
* Added rfc7951 parameter to `clixon_json_parse_string()` and `clixon_json_parse_file()`
* If set, honor RFC 7951: JSON Encoding of Data Modeled with YANG, eg it requires module name prefixes
* If not set, parse as regular JSON
* Test: added test_db.sh for datastore format tests