Suggestion: Add limit alarm severity settings to UI

[ZLLentz]

We had some analog PVs whose alarm settings were not configured:

zlentz@las-console:~$ caget LM1K4:QADC:01:OUT0_EDGE1.HSV
LM1K4:QADC:01:OUT0_EDGE1.HSV   NO_ALARM
zlentz@las-console:~$ caget LM1K4:QADC:01:OUT0_EDGE1.LSV
LM1K4:QADC:01:OUT0_EDGE1.LSV   NO_ALARM
zlentz@las-console:~$ caget LM1K4:QADC:01:OUT0_EDGE1.HHSV
LM1K4:QADC:01:OUT0_EDGE1.HHSV  NO_ALARM
zlentz@las-console:~$ caget LM1K4:QADC:01:OUT0_EDGE1.LLSV
LM1K4:QADC:01:OUT0_EDGE1.LLSV  NO_ALARM

The users had set values to LOLO, LOW, HIHI, and HIGH, but apparently EPICS does not propagate these alarm limits to the PV metadata if the severity settings are set to NO_ALARM, which is the default. In these cases the alarm limits display as nans via caput and as "Not set" in the "Display Alarm Thresholds" context menus here, which is absolutely correct but we could be more helpful.

Our users may have been able to figure this out themselves if the UI displayed something like:

HIHI: Not set, HHSV: NO_ALARM
HIGH: Not set, HSV: NO_ALARM
LOW: Not set, LSV: NO_ALARM
LOLO: Not set, LLSV: NO_ALARM

And then when properly configured, something like:

HIHI: 10, HHSV: MAJOR
HIGH: 5, HSV: MINOR
LOW: -5, LSV: MINOR
LOLO: -10, LLSV: MINOR

Or any other superior variant of this that makes it clear that the record isn't configured for a limits alarm.