Fix sort order of recent files in startup dialog

We want to make sure the user can find the latest files they have modified when using the start screen. So we sort them by their last modified date.

Other improvements are recording when inkscape crashes the crash file in the RecentManager which can be detected by the startup screen and labeled.

This allows users to open crash files and keep working as if they were the original file. The opened document is redirected to the original filename and marked as dirty to indicate it needs saving.

There's a new action which allows you to crash Inkscape for testing. Press '?' and search for "Force Crash"

Fixes #4081 (closed)