Bugfixes and improvements

Fix application crash when using the command core:restart.

Improve application startup to avoid flashing window's problem.

Fix a few problems with documents' filenames.

New plugins versioning

Move to new plugins versioning scheme using tag mod-version:1.
The mod-version is a single digit version that tracks the plugins compatibility version independently from the lite-xl version.

For backward compatibility the tag -- lite-xl 1.16 is considered equivalent to mod-version:1 so users don't need to update their plugins.

Both kind of tags can appear in new plugins in the form:

-- mod-version:1 -- lite-xl 1.16

where the old tag needs to appear at the end for compatibility.

New contributors

This release includes some improvements from a new contributors @adamharrison, welcome onboard!