Show versions appropriate for board type on Install Firmware

With the APM1/2 coming towards end-of-life at least for the arducopter code (arduplane and ardurover will probably continue longer) we will need to be able to show different versions for different boards. So if an APM2 is connected, the version number will likely remain at AC3.2.x while for the Pixhawk, VRBrain, etc it will continue beyond that.

It's not an urgent problem as AC3.2 isn't even out yet and it won't be a real problem until we hit AC3.3 at which point the versions will diverge.

Start at the Install Firmware screen and trace how the connected board type and available firmware versions are selected. Compare the expected behavior for APM1/2 versus Pixhawk and VRBrain, then verify that each board shows only appropriate versions and that the existing installation flow still works.

Written by the indexing model from the issue text.