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[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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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