* Handle RTL text
Fixes issues related to dropdown menus (right align instead of left align), and bi-directional blocks (e.g., go to x: %1 y:%2, the ‘x: %1 y:%2’ is LTR, but should not be treated as LTR, when rendered in Hebrew it should be ‘%2 :y %1 :x’)
* Set dropdownDiv direction
Set the direction based on the rtl of the block that owns the menu.
Note the css for dropdowns is completely different from blockly (`float` vs `absolute`) as a result of this PR from a couple of years ago: https://github.com/LLK/scratch-blocks/pull/632/
* use right-left-embed (rle) unicode to force RTL text, and left-right-embed for editing numbers.
* Refactor drop-down positioning to encapsulate block positioning
Moves block-positioning logic to the DropDownDiv class. Since icon menus use a special offset for the secondary mode, add an option for that.
* Swap out field_dropdown's use of WidgetDiv with DropDownDiv
* Update CSS for goog-menus in DropDownDivs
* Fix hiding behavior when showEditor_ is called again
* Icon menu and drop-down stubs
* Recompile 4/15
* Fix stubs to draw shadow block for drop-down
* Fix rendering of shadow for icon menu
* Add arrow to dropdown button
* Add drop-down buttons to rest of examples
* Implementation of drop-down div including positioning
* Drop-downs take colours from the blocks
* Fix scaled secondary position of drop-downs
* Fix arrow positioning for RTL
* Use SVG parentNode for sizing dropdown
* Use transform for drop-down positioning
* Add basic DropDownDiv hide
* Add animation-in to dropdown
* More subtle drop-down animation and shadow
* Add icon menu example
* Use options style of Blockly FieldImage for drop-down
* Add default value for iconmenu
* Add example hover, active states for iconmenu buttons
* Update dropdown_icon example
* Implement icon-menu value handling and default value
* Add updating the parent block image field to dropdown
* Drop-down animates out; add hooks to hide for various Blockly happenings
* Add pointer cursor for drop-down icons
* Improve documentation for drop-downs and minor refactor
* Factor out getSrcForValue in iconmenu
* Blocks take on the icon of their icon-menu
* Add basic accessibility properties, similar to closure
* Remove extra drop-down example; update playgrounds
* Remove unnecessary colour overrides
* Add onHide, colour changing, fix references in dropdowndiv
* Flip arrow when the drop-down is rendered above
* Hide the icon menu drop-down on second tap of button
* Add preventDefault to button ontouchstart
* Updates to drop-down from Carl
* Add icon-menu placeholders and a crazy demo
* Fix naming to normalize (drop-down, DropDown)
* Add license header