Performance optimations

A whole slew of macro and micro optimizations. These are generally non breaking but there are a few changes that may break some workflows.

1. Users building with lumbar who desire the forms feature must include the thorax-form mixin
2. The `helper:$name` event has been removed. Users should bind to the `helper` event and check the name parameter that they wish to examine.
3. `_.uniqueId` no longer uses global variables for tracking state. Instead callers must call `_resetIdCounter` when wishing to modify that behavior.
4. `context` no longer clones the model attributes so callers need to take care to not modify the returned value.
micro opt: Avoids indexOf lookup for `index === 0` case. Likely fast but felt like a why not avoid the call sort of case.