Add option to convert templates to Device without header

[GDYendell]

This is a breaking change to the convert device CLI.

Change header from required positional arg to option --header.
Add --name and --parent args to specificy without header.
Add --label to override UI label of Device.

Fixes #120

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.78%. Comparing base (a8e884c) to head (013be18).

Files	Patch %	Lines
src/pvi/__main__.py	85.71%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #125   +/-   ##
=======================================
  Coverage   89.78%   89.78%           
=======================================
  Files          23       23           
  Lines        1449     1459   +10     
=======================================
+ Hits         1301     1310    +9     
- Misses        148      149    +1     

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