Use icons for ScanServer Monitor low mem and idle display

[DomGarguilo]

fixes #6184

This PR adds icons in place of 1 and 0 in the ScanServer table in the Monitor UI. I also updated the title for these columns to better match this new display:
low mem -> Memory State
idle - Activity State

I was not able to trigger the low memory manually but this icon will be present in color warn (yellow) when that value indicates low mem:
https://icons.getbootstrap.com/icons/exclamation-triangle-fill/

I am open to other ideas for which icons to use if anyone has a preference. These were the ones that made sense to me but might not be the best fit.

[dlmarion]

No issues here with the changes. All of the server types should be reporting these metrics (idle, low mem), so I'm not sure if the code changes should be in a more central place or not.

[DomGarguilo]

All of the server types should be reporting these metrics (idle, low mem), so I'm not sure if the code changes should be in a more central place or not.

Could move things. The sserver page is the only place in the monitor where either of these is displayed at the moment. I think if we want to add those data points to other pages that is reasonable and in that case I think its a good idea to centralize this logic.