mqtt module update

[Towflos]

I simplified the convert_to_dict function and added the option to use a username and password for authentication

[peterbarker]

@Towflos please squash this all into a succinct set of commits, one per logical change (or, really, just one with a good commit message.

Let me know if you need help doing this; the ArduPilot page on interactive rebase might help you, 'though: https://ardupilot.org/dev/docs/git-interactive-rebase.html

Commits should be prepended with mavproxy_mqtt: on the first line

[Towflos]

@Towflos please squash this all into a succinct set of commits, one per logical change (or, really, just one with a good commit message.

Let me know if you need help doing this; the ArduPilot page on interactive rebase might help you, 'though: https://ardupilot.org/dev/docs/git-interactive-rebase.html

Commits should be prepended with mavproxy_mqtt: on the first line

I think I need some Help with this. I squashed all the commits into one and changed the message. Do I also need to delete the old commits?

[peterbarker]

@Towflos I just had a go at fixing this; the fixes are not trivial, and I'll probably break something. Bit of a mess in here :-)

I suggest that you:

• stop using your master branch for creating new code, instead use "topic branches" (google, or bits on our Wiki on git will help there)
• take a branch of your work here (git branch pr/mqtt-fixes-defunct master)
• reset your master branch to origin using git checkout master; git reset --hard origin/master
• create a new branch based on master (git checkout master; git checkout -b pr/mqtt-fixes`and do your work again on that branch, perhaps based on what's in that backup branch

Reasonably urgently we need to stop this module from using f-strings and make sure it at least compiles under Python2

f-strings seem to be awesome, just not yet in MAVProxy :-)