Port of a major refactor from Blockly. Dragging logic now lives in block_dragger.js, gesture.js, workspace_dragger.js, dragged_connection_manager.js (unused by scratch-blocks), and insertion_marker_manager.js (used only by scratch-blocks).
* WIP: New zoom controls
* Adjust sizing as per discussion with Carl
* Update icons and spacing as per discussions with Carl
* Remove unused 'rnd' function
* Updated icons
* Resolve issues from PR review
* WIP merge from upstream google/blockly
* fixing some merging bugs. Getting the drag surface to work, updating some function calls, etc.
* make the trash can lid animate again and fix the cursor to show an x when things will be removed.
* Fix text rendering logic in fields
* Hand apply some more changes from blockly flyout.js to flyout_base.js.
Also revert 08efd1381c
in scratch-blocks since it breaks variables and there is more work fenichel is planning
to do here.
* Fix drop-down field rendering
* Resolve issue with text input field widths on init
* Remove unused blockly (built) files
* Remove unused language files
* Resolve lint issues and rebuild
* Add blockly build targets to cleanup script
* Return 0 if 'this.arrow_' does not exist in a dropdown field
* Remove unused / irrelevant comments
