Fix colors and diagnostics naming

[MCFurry]

First of all, thanks for your great project. Rosboard is a really useful app!

There's some minor things I personally like better about the diagnostic_viewer this way:

• The standard robot_monitor from rqt groups diagnostics by root name, rosboard does that by hardware_id. I like the name grouping better, this also allows for multiple instances of the same hardware, and gives the same result as rqt's robot_monitor.
• If an entry has more key-value pairs in sub-groups, only the last list shown on rosboard, with this PR all pairs are collected by not starting with an empty object if it exists already
• The colors didn't seem to work, but when applying the colors to the text instead it does show

[Timple]

Good day, is there any update here? Or are there perhaps any objections to address?

[Timple]

ping?

[dheera]

Thanks! Sorry I've been dealing with a bunch of work and life changes recently so I've been slow here!

[MCFurry]

Thanks!