Updated delete icon to Material Design

Copied from the official Google Material Design icon repo
Initial version of simplified Graph demo.
Completed Graph demo.
Redirect Maze and Turtle to Blockly Games.  Redirect Graph to demos.
Move Plane app to demos.
Merge branch 'master' of https://github.com/google/blockly

Conflicts:
	apps/json/en.json
Add momentary highlighting to Plane's language menu.
Move Code app to demos directory.
Remove core-unsupported languages from Code demo.  Fix resize in Graph.
Fix redirect on Code demo.
Fix illegal connections in stacks after a healing delete (issue 15).
Merge pull request #11 from JordiOrlando/master

Update delete icon to Material Design

Google has always been suspicious of the old trashcan artwork.  It came from MIT's Open Blocks, which despite claiming to be open source is known to have some copyrighted resources (click sound is stolen from MS Windows 95).  A thorough search could not locate any known origin for the trashcan, so we used it, warily.
Fade out trashcan when closed.
Add separators to toolbox.
Add XML unit tests.
Add red 'X' to mouse cursor if blocks are over the trash can.
Add red 'X' to mouse cursor if blocks are over flyout.
Convert Blockly.Toolbox from a singleton to an instance.
Fix coordinate bug introduced yesterday.
Use existing path constant for notch highlighting (issue #18).