(bug 44755) language terms table has now edit features in JavaScript UI

* Initialization of EditableValues for terms table values in wikibase.ui.entityViewInit.js
* New option for EditableValue, 'valueLanguageContext' , which allows to define the language of
  the editable value in case the value is multilingual (e.g. label/description/aliases). Comes
  with a new static function, wb.ui.PropertyEditTool.EditableValue.getValueLanguageContextFromDom,
  which tries to extract the language from given DOM.
* Cleanup of 'wb-term' template, removed DOM overhead.
* Updated some documentation related to EditableValue.

Known Bugs, to be resolved in follow-ups:
* Edit mode does not yet trigger global edit mode, so other edit buttons can still be hit while
  editing values in the language terms table.
* After editing one of the values in the language terms table, clicking edit on the same value
  again, editing won't be possible because the input is disabled.
* The help tooltips are incorrect.

- patch set 2: minor formatting/doc update

Change-Id: I0f9661626e56275672fc26250c70b2f9ff010e31
Merge "(bug 44755) language terms table has now edit features in JavaScript UI"