Add support for mug interaction with data tree writer
Allow mug to interact with control tree writer
Clean up label writing
Writer: moving code around

Move createOpenControlTag out of createControlBlock
Move mug-specific writer options into mug options
Refactor writer so Repeat is no longer special
Refactor writer so ReadOnly is no longer special
Merge branch 'model-repeat-writer-refactor' into help-text+model-repeat-writer-refactor

Conflicts:
	src/writer.js
Improve docs for mug writer integration
Abstraction for writing extra data attributes
Merge pull request #288 from dimagi/model-repeat-writer-refactor

Model repeat writer refactor