Homing: improve homing and feedback on user interface

[FreddieAkeroyd]

When homing an axis I would like the user interface to report what is going on better. Specifically:

• is an axis currently homed (and if possible when that was)
• unhomed axes show in alarms view?
• when did the controller last power cycle (which will also affect homing, unless absolute encoders)
• did the home i had just tried to home complete successfully or fail (time out)
• limit lights come on as expected during home (see Hitting a limit switch whilst homing displays incorrectly #5868)
• the home icon meaning is clarified. It may mean "at home" but on some axis it is on all the time and others never on except briefly when it passes a home switch
• fix issue with multiple same galil axes homing at once, or stop such things being requested from the gui. These can lead to a homing timeout, so it may be enough to just clearly flag failed homes as above.

[FreddieAkeroyd]

See #8350