Clean-up of main repo 4

[johanneskbl]

What is this

Clean-up and documentation of aerial_robot_base.

Details

• commit1: Renaming of 1/main_rate = main_loop_dt
• commit2: Fix declaration and move to header file

TODO

• In my opinion, variables that indicate time should be named with "t". There are multiple other variables in the rest of the code base to use "u", e.g. "loop_du", instead. Since "u" is generally reserved for the control input I would propose to change all those variables to make it easier to understand the code more intuitive. I'm open to be convinced otherwise :)