Rename Command and Update enum values for clarity and consistency.
Reverted LOG_IN & LOG_OUT back to LOGIN & LOGOUT for consistency.

If we fix the spelling later we should fix it in the whole codebase to
maintain consistency.
Merge branch 'dev' into matthild_polish_message_names
Merge pull request #382 from uProxy/matthild_polish_message_names

Rename Command and Update enum values for clarity and consistency.