app version shown in About is not linked to repo tagging

[Robotmad]

ideally we would put the version text _APP_VERSION into the released application based on the tag given to the release (keep it short so that it fits in the place allocated on screen). i.e. only X.Y (and ignore lower level digits)

[Robotmad]

This is independent of CURRENT_APP_VERSION (which should perhaps be renamed to identify that this is the app on the HexDrive EEPROM) which is more of an identification of the API version that is provided by that code for using the HexDrive. i.e. the main app version could easily increase without any change to the API (hopefully that can remain quite stable).