Reimplementation of collapsible calculator panel

This pull requests reimplements the calculator panel:
- the collapsible toolbar panel is now also a freely movable "toolbaritem" (the same as for PanelUI)
- antiquated and deprecated "statusbarpanel" is dropped
- Styling (collapsing, animations, etc.) is done soley in CSS, so there is minimal need for custom JS code
- thereby: reduced code complexity, improved compatibilty, increased flexibility

Also
- some minor changes to localizations
- higher resolution icon
- some minor cleanup of code / typos in comments