Transitions

Closes #75

- Adds slide left, slide right, and fade transition support for activities
- Transitions are defined in xml files
- Simplified AsyncStateUtil into ActivityUtil
- Return to delegate on error via TahoeActivity
- Adds User#saveAndPublish as well as an identical method for Request
- Simplified Channels by taking a TahoeApplication instead of Handlers
Merge pull request #148 from steffanc/75-animated-transitions

Transitions
Implement dialog blocker between async calls.