Use it before loading projects so targets don't accumulate when multiple projects are loaded on the same instance.
Move check to see if the clone is the original clone onto the block implementation so all clones can be removed.
Fixes#274
* Implement "go to" block
* Add a missing semicolon
My text editor doesn't automatically insert them and I'm not used to using
semicolons so much. :(
* Implement go-to-random
* Clean up the go-to-random code a bit
* Add rounding to _random_ picks
* Add scratch3_procedures and no-op for defnoreturn
* Add mutation adapter to parse mutations in CREATE/CHANGE events
* Add mutation-to-XML
* Update spec map for Blockly procedure names
* Placeholder for procedure special cases
* Basic stepping to procedures
* Remove extra case
* Validation for changeBlock
* Import lists and variables from SB2
* Switch to Variable and List objects
* Add Clone.lookupOrCreateVariable, Clone.getVariable, Clone.setVariable
* Add (get, set, change) variable blocks.
* Copy variables and lists on clone instantiation
* Move variable options closer to blocks
* Add list primitives
* Move variable and lists storage to `Target` instead of `Clone`
* Move _computeIndex to a Cast function
* Rename `getList` -> `getListAsString`
* Renames renames
* Remove extra check in Cast.isNaN
* Provide property to Clone to distinguish "original" clones
* Provide method to clone a clone's properties
* Don't report clones in the UI target list
* Add target info to Thread
* Allow hats to skip clones (for green flag)
* Green flag skips clones
* Implement "create clone" and hat
* Pass the runtime to sprites and clones (for start hats)
* Clone disposal; trigger hats after drawable initializes.
* Separate stop threads for target; fix handling of stop button
* Remove extraneous `skipClones` property
* Add global clone limit
* Don't allow a non-clone to delete itself.
* Rename `cloneClone` -> `makeClone`
* Variable updates in runtime.js
* Synchronous drawable initialization (until we put it back to promises)
* Strip out old script glowing in thread management
* Add new tracking mechanism for glowing scripts
* Track parents and use them to determine script glows
* Use top-block for a thread if there's nothing on the stack
* Remove `console.log`
* Add `Clone.prototype.getCostumeIndexByName`, keep in range
* Add basic costume primitives from Scratch 2.0
* Add costume getter block
* Add properties and methods for distinguishing stage and sprites-vs-clones
* Add backdrop-related looks blocks
* Fix up "switch to backdrop" to be working
* Costume/backdrop reporters are 1-indexed
* Fire "when backdrop switched" hats
* Cut cloning helpers for a separate PR
* Disable many blocks on the stage
* Refactor into _setCostumeOrBackdrop; implement switch backdrop and wait
* Fire hats even when backdrop unchanged
* Key pressed hat
* Tabs -> Spaces
* Oops
* Edge activate
* Fix hat
Phew...
* I forgot to change it also here
:/ :/ :\
* Minor fixes for TravisCi
* Minor docs
* Line length
