LibreSignage v0.2.2 patch release

This is the second patch release in the LibreSignage v0.2.x
series. This relese contains fixes for many important bugs.

Changelog

- [bugfix]   Fix a bug that prevented removing slide assets that didn't
             have a thumbnail.
- [bugfix]   Fix dialogs not appearing correctly on the documentation
             pages.
- [bugfix]   Fix a bug where adding media to user-created slides didn't
             work. (#27)
- [feature]  Implement a new tag [font] in the markup transpiler for
             changing fonts in slides. (#28)
- [bugfix]   Add a missing class definition that caused problems when
             uploading files.
- [bugfix]   Fix a bug where the editor media uploader popup didn't
             close if the (X) button was clicked after an upload had
             failed.
- [feature]  Allow space characters in upload filenames.
- [bugfix]   Implement automatic slide lock cleanup on logout.
This tag has no release notes.