[EditInPlace] Add contextual informations when editing

[damienalexandre]

When editing a translation via EditInPlace, we should use the status bar of ContentTools (at the bottom of the page) to display contextual informations about the current editing:

• the full translation key
• the translation domain
• all the available variables (placeholders, parameters, transChoice)
• maybe the other languages alternatives?

This will mainly require JavaScript to extend the ContentTools Inspector UI https://github.com/GetmeUK/ContentTools/blob/master/src/scripts/ui/inspector.coffee

[rvanlaak]

Would also be great to:

• add a link to the Web UI translation page directly