Add Robot class tests

[sea-bass]

This PR adds unit tests to the Robot class, and fixes a handful of issues in doing so.

I also took the liberty of

• Moving some test files around (one of them was sitting with the source code)
• Using pytest.warns to reduce the number of warnings produced by running the whole pyrobosim test suite.

Closes #93

[ibrahiminfinite]

Maybe we should pull out the world object outside as a non optional argument called map
Rest of the config can be optional. I feel that would make for a more intuitive API.
What do you think @sea-bass ?

[sea-bass]

Maybe we should pull out the world object outside as a non optional argument called map Rest of the config can be optional. I feel that would make for a more intuitive API. What do you think @sea-bass ?

That seems reasonable (it also makes the switch from world/grid easier) -- but not in this PR, if that's OK?

[ibrahiminfinite]

Yeah, definitely not in this PR.