Use new fixed position admin messages and add --remove-position argument

[ianmcorvidae]

Fixes #525

Pending more restructuring of the CLI, of course, but I've put off fixing this particular thing long enough, I think.

[ianmcorvidae]

Right, the other thing I did was allow setlat/setlon to take integers premultiplied by 1e7. Should allow a little more flexibility, hopefully, but willing to remove if we think it'll be problematic.

[codecov]

Codecov Report

Attention: Patch coverage is 42.55319% with 27 lines in your changes are missing coverage. Please review.

Project coverage is 61.31%. Comparing base (4d67e7f) to head (1746ad1).

Files	Patch %	Lines
meshtastic/node.py	12.50%	21 Missing ⚠️
meshtastic/__main__.py	73.91%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #584      +/-   ##
==========================================
- Coverage   61.81%   61.31%   -0.50%     
==========================================
  Files          14       14              
  Lines        2941     2973      +32     
==========================================
+ Hits         1818     1823       +5     
- Misses       1123     1150      +27     

Flag	Coverage Δ
unittests	61.31% <42.55%> (-0.50%)	⬇️

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