Adding support for string table lookups in dropdown field labels specified in JSON.
Adds Blockly.utils.replaceMessageReferences() method to handle string replacement without interpolation tokens. Effectively uses the same old code, now moved into tokenizeInterpolation_(), which takes a parseInterpolationTokens option.
Replaces the direct JavaScript references (not pure JSON, and thus not portable).
Demonstrating this behavior in the logic_boolean dropdown.
* Add a workspace drag surface that blocks and bubble get moved to during a workspace drag.
The surface is translated using translate3d instead of svg's translate attribute so that
the browser does not have to repaint the entire workspace on every mouse move.
This is very similar to the block drag surface.
* Address code review comments
* add back hasClass_ utility removed in #748 and stop using contains since it is not supported in IE
* Adds message references to message string interpolation, in the form of %{BKY_STRING}.
* Re-adding CONTROLS_IFELSE block using the new syntax, referencing to CONTROL_IF equivalents.
