Add one-time callback registration
Re-factor isSensorConnected() to be async
More async refactor
Fix errors when clicking start
Need to use the new java code
Various sensor applet fixes

Fix code path where callback is never called.
Gracefully handle overlapping readSensor calls.
Handle state in readSensor better.
Update experiments to use new async sensor applet code
Fix error in clearing callbacks after use

We definitely shouldn't be clearing class instance methods!
Sensor applet start needs a callback so we can propogate errors
Remove unneeded javascript
Merge branch 'master' into wip-async-sensor
Fix branch name for sensor-applets java project
Start callback is optional
Merge branch 'master' into wip-async-sensor
Merge pull request #47 from concord-consortium/wip-async-sensor

Asynchronous sensor applet interactions