Split `if` helper test into a separate file
Add tests for attribute hook/helper.

* Add tests to confirm we are using `setAttribute` for some level of
  escaping (equivalent to what we have today with `{{bind-attr}}`).
* Updated to ensure that rerenders happen in the `render` queue.
* Added dirty tracking to not needlessly update attributes.
* Move `attribute` and `concat` to separate `helpers/` files.
* Changed `lookupHelper` to be a default export.
Update to HTMLBars 0.1.5.
Merge pull request #9669 from rwjblue/htmlbars-update-master

Update to HTMLBars 0.1.5.
Merge pull request #9668 from rwjblue/htmlbars-attribute-tests

Add tests for HTMLBars attribute hook/helper.
Update to latest HTMLBars.

* Add compiler options to allow disabling component generation.
* Implement quoted and unquoted attribute semantics.
* Rewrite attribute helper as a hook.
* Add `DomHelper.prototype.removeAttribute`.

Compare view:
https://github.com/tildeio/htmlbars/compare/v0.1.5...v0.1.7
Merge pull request #9672 from rwjblue/htmlbars-update-attribute-hook

Update to latest HTMLBars.
[FEATURE] ember-htmlbars-component-generation

Disable HTMLBars `component` hook unless this feature is enabled.
Merge pull request #9673 from rwjblue/htmlbars-disable-component-generation

[FEATURE] ember-htmlbars-component-generation
Merge pull request #9657 from twokul/handlebars-test-split

Moves `if` and `unless` helpers tests into a htmlbars tests
Ensure that initially null attributes are not added to element.
Merge pull request #9674 from rwjblue/htmlbars-initially-null-attributes

Ensure that initially null attributes are not added to element.