add parse_cmip5 & parse_cmip6 functions

[mathause]

Everything is in cmip.py - we just have to make it explicit

This is used in

https://github.com/IPCC-WG1/Chapter-11/blob/d1a3a99f242a568fb4cefc36a038c888a90b9d37/code/utils/cmip_conf.py#L622-L627

[mathause]

Should also re-think the ensnumber - as it may be misinterpreted. It numbers the available ensemble members - thus a given rXiXfXpX can change it's ensnumber. But I am also not sure what to use otherwise...