Make several dependencies optional (dotmap, print_color, and pyqrcode)

[ianmcorvidae]

This should assist with packaging, especially in more limited environments such as openwrt and buildroot.

• dotmap is only used by the meshtastic.test namespace, so now it's imported in a try-catch block
• logs will only be printed in color if print_color is installed
• the QR code will only be printed if pyqrcode is installed, but users will be pointed to install it if they want (the QR code options still print the URL itself out)

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 60.22%. Comparing base (89b41c1) to head (4673824).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
meshtastic/__main__.py	68.42%	6 Missing ⚠️
meshtastic/mesh_interface.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #711      +/-   ##
==========================================
- Coverage   60.29%   60.22%   -0.08%     
==========================================
  Files          24       24              
  Lines        3816     3829      +13     
==========================================
+ Hits         2301     2306       +5     
- Misses       1515     1523       +8     

Flag	Coverage Δ
unittests	60.22% <62.50%> (-0.08%)	⬇️

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