Better integration with angular

Baobab by default batches up the notifications about changes to the immutable stores into the next tick to improve performance. However, since the next tick is outside the angular digest cycle this led to cases where the emit was not caught by angular. Now all $listenTo callbacks are wrapped in $evalAsync by default to ensure angular is alerted of the Baobab changes. For most users this should just make things more reliable, but users will still want to test that there are no adverse effects. The old behavior can be re-enabled by setting fluxProvider.useEvalAsync(false);