Rename protected methods to retain pre-2020 backwards compat

[virtuald]

.. ironically a breaking change for 2020 which I don't usually do in the middle of the season, but long term this is better?

@picode98 and @benjiboy50fonz do you have opinions on this? The effect would be most of the command stuff would be back as it was previously, instead of protected methods starting with underscores.

@auscompgeek may also have sage advice.

[auscompgeek]

I think this mostly makes sense: this is, for the most part, the "public" interface.

Might be better to just have a switch at the class level to turn off the protected prefixing though (and/or at the package level).

[FRC2539]

We vote to remove the underscores

[picode98]

For functions like _execute and _isFinished in Command, implementing them as public members makes more sense to me, especially since the scheduler (an external class) is calling them.