Refactor mod to follow best practices better

[tckarenchiang]

Since we have quite a number of additional lua files, sometimes it's hard to find the right file.

We should categorize them into different sub-directories of the lua folder.

E.g. all ros messages helper functions into a folder called ros_messages, etc.

[gavanderhoorn]

@tckarenchiang: I've updated the title of the issue to change the focus, as I believe it would be good to refactor the mod in its entirety to follow best-practices better instead of simply moving files around.

There are some good quality mods which we could use as inspiration/templates (Seasons, Courseplay, GuidanceSteering).

[gavanderhoorn]

#41 also works towards this.