Add validation/prevent --set-owner, --set-owner-short, and --set-ham …

[Crank-Git]

…from accepting empty or whitespace-only names. This is in relation to feature request meshtastic/firmware#6867.

Added test validation and when trying to set long, short, and ham names we get the following via the cli:

python -c "import sys; sys.argv = ['', '--set-ham', '   ']; from meshtastic.__main__ import main; main()"
ERROR: Ham ID cannot be empty or contain only whitespace characters

python -c "import sys; sys.argv = ['', '--set-owner', '   ']; from meshtastic.__main__ import main; main()"
ERROR: Long Name cannot be empty or contain only whitespace characters

python -c "import sys; sys.argv = ['', '--set-owner-short', '   ']; from meshtastic.__main__ import main; main()"
ERROR: Short Name cannot be empty or contain only whitespace characters

Please let me know if there is anything else that I should add or modify. I have no idea what I am doing with Android SDK/development, so I believe someone will need to add this validation so the app also gives an error/warning when trying to set these.