Allow 0s in <AxisInputBox/>, unlink Y/Z coords

[RickCarlino]

What's New?

• Fix bug where entering 0 results in -1 on AxisInputBox
• Prevent Z axis from "linking" to Y axis.

[codecov]

Codecov Report

Merging #359 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #359   +/-   ##
=======================================
  Coverage   95.85%   95.85%           
=======================================
  Files         125      125           
  Lines        1880     1880           
=======================================
  Hits         1802     1802           
  Misses         78       78

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[coveralls]

Coverage increased (+0.08%) to 21.14% when pulling f65003d on RickCarlino:master into 9d0c9e4 on FarmBot:master.