fixed null pointer error

Change-Id: Ib55fce30b15bfa807c3deea8e14ccb16ffb42b56
updated documentation

Change-Id: If92b573b9a5d6d8e1e14dc6c29814ba89f128868
Now resetting callback variables to previous values instead of null.

Change-Id: I2f00fea5c1cb22166ff113ba626be44ccc5ed2d1
Moved StageUtils event callback functionality into separate internal
class. Fixed bug where event variable may be unset if an event was
interrupted by code from a JavaScript popup window.

Change-Id: I9add805f9a32477e6686080ba1f9da3008a8adf2
Separated class registry functionality from WeaveAPI into
ClassRegistryImpl and eliminated some mx dependencies.

Change-Id: I63a42c45ca447b826ffc1032476abdfcdac0c8fd