Update changelog and messages.json for v0.5.0
Finish v0.5.0
Add insert_date_panel command

Opens a panel with pre-defined settings and previews them
Update keymaps and docs on the panel addition
Add an id to the InsertDate menu entry

This will hardly find any use, but whatever.
Update changelog and messages.json for v0.5.1
Finish v0.5.1