Polish and document internationalisation

[tpluscode]

Any text displayed by Shaperone should be translateable so that it can be easily switched and automatically adjusted according to browser locale

Work in progress, with some features incomplete or buggy

• [x] Display Property Shape labels in the right language
• [ ] Translations of other static text
• [ ] Display labels of resources displayed by dash:InstancesSelectEditor etc

Some issues found to date

• [ ] In some scenarios, switching language does not update select boxes