GUI: LivePVTableModel additional features

[tangkong]

Current Behavior

The LivePVTableModel in #72 is functional, but could use some quality of life features

Expected Behavior

core functionality

• tolerance and read-only columns
• Editable fields (for modifying entries once they've been added)

Nice-to-haves

• Click-and-drag column rearranging
• Hierarchical columns for condensing live/stored values
• Methods to show/hide columns easily
  • a right-click context menu that lets the user do this
• Color coding of the enum values (Status, severity). RGY is probably enough to show statuses that are bad/good/off-normal respectively

Context / environment

Features that took too long in #72 but are probably quire valuable for the user

Steps to Reproduce (for bugs)

N/A

Suggested Solution

Hierarchical headers is quite involved, we probably vendor something like this: https://github.com/Winand/dataframemodel/. This probably has the worst benefit-to-effort ratio
Click and drag features probably have the next worst benefit-to-effort ratio, would involve some amount of click-event hooking.

I'd prioritize color coding and show/hide functionality to start, along with show/hide methods

[tangkong]

Reminder: Needs to also refactor other bits that hide columns, for example in #80