Release 3.37.1, 2020-04-24
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* User-visible changes:
- Use TeplPanel to create the side panel. This changes the UI for switching
  between side panel components, it's now like a toolbar (so only a single
  click is needed), before it was with a GtkComboBox list (so with two
  clicks).
- Search and Go to line: better style for the text entry's not-found state.
- More beautiful close buttons at some places.
- Use some Tepl I/O error info bars.
- Translation updates.

* Under the hood changes:
- Port to TeplMetadata.
- Use TeplStatusbar.
- Use TeplStyleSchemeChooserWidget in the preferences dialog.
- Subclass TeplAbstractFactory, not TeplAbstractFactoryVala.
- Move more utility functions to Tepl.
- Remove some dead code.
- Remove no longer useful code related to stock icons.
- New classes in the liblatexila (so in C): LatexilaFactory, LatexilaSettings.
- Statistics for the Vala code, compared to version 3.36.0:
       - 4 fewer *.vala files.
       - 579 fewer Vala lines of code.