Add support for polygon sprites

Rotation, collision, and bounding box are done. Scaling needs to be done
later.
Testing an added set volume block
Add pong demo
Merge pull request #327 from pikalex88/318_music_blocks

Added a set volume block
issue #328, fixed save/load of local names
Merge pull request #329 from dannywils/master

Add support for polygon sprites
fix for missing sibling element
resolved merge conflict by rebuilding
fix for #352
Merge pull request #353 from waterbearlang/352_autofocus_canvas

fix for #352
fix merge conflict
quiet spurious missing file warnings from build script
fix pong example corrupted in earlier merge
add support for running examples
Merge pull request #354 from waterbearlang/support_running_examples

add support for running examples
Updated pong example to have matching variable names on restore
Merge pull request #355 from klindenbach/master

Updated pong example to have matching variable names on restore
Got a context menu that behaves like a menu and only appears when right-clicking a block.
- Menu items are non-functional however.
Context menu items are now selectable and do something!
Not anything useful yet, though.
- The menu can also be disabled so that the user can easily access the browser's right-click menu if they want to.
issue #264, converted ask and wait block to expression from step