Update Help messages to be more controller agnostic

[justinclift]

Just noticed the description lines in the Help section specifically refer to GRBL. This PR just replaces "GRBL" with "the controller" so it's a bit more controller agnostic. 😄

Note - I made these changes blindly, without testing if the result compiles ok. Merging blindly is probably not a good idea. 😀

[codecov-io]

Codecov Report

Merging #1075 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1075   +/-   ##
=========================================
  Coverage     30.08%   30.08%           
  Complexity     1087     1087           
=========================================
  Files           153      153           
  Lines         10429    10429           
  Branches        943      943           
=========================================
  Hits           3138     3138           
  Misses         6988     6988           
  Partials        303      303

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[winder]

Thanks @justinclift. That's what the continuous integration servers are for :)