Add autocomplete for questionnaire/mapper

[ruscoder]

While entering resource fields, e.g. enableWhen, item, launchContext, calculatedExpression autocomplete should be enabled.

[ruscoder]

It can be done using https://codemirror.net/examples/autocompletion/
But it should be smarter than just suggesting all available keywords for every word: enableWhen should be shown only inside item, and launchContext should be shown at the root level.

[ruscoder]

Some intermediate results