Set alarm levels of blocks from genie_python

As a user, I would like to be able to change the high/hihi/low/lolo alarm levels (for numeric records) and enum severity levels (for enum records) and their severities from a script.

This was asked for by James referring to RIKENFE, where they would like to be able to define alarm levels in their `set_magnets` script. The alarm levels would change frequently, so we can _not_ hard code these.

This probably belongs in the "advanced" genie module, something like `g.adv.set_alarm_levels(...)`