Fix svg icons display issue in plugin list and plugin detail

[Xpirix]

• This PR is for the following issue: #65

Changes summary:

• Show SVG icons directly in the plugins list and the plugin detail page since solr-thumbnail doesn't support them

QuickOSM is an example of a plugin that uses an SVG icon:

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6d03c84) 36.94% compared to head (e0dc8e2) 82.68%.

Files	Patch %	Lines
qgis-app/plugins/templatetags/plugin_utils.py	50.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #348 +/- ## =========================================== + Coverage 36.94% 82.68% +45.73% =========================================== Files 106 142 +36 Lines 4504 5503 +999 =========================================== + Hits 1664 4550 +2886 + Misses 2840 953 -1887 ```

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[Gustry]

Thanks @Xpirix ! 👍

[Xpirix]

My pleasure.