When an HWPI theme is enabled, enable breadcrumbs

#3848

#### Changes

* add optional param to `_is_hwpi_theme()`
* add form submit to change breadcrumbs variable when hwpi theme is enabled
* add help text to breadcrumbs setting, use checkbox (not radios)

##### before:

![screen shot 2013-10-04 at 3 05 38 pm](https://f.cloud.github.com/assets/228733/1272381/3bdfb328-2d2e-11e3-9030-b3ef449336ac.png)

##### after:

![screen shot 2013-10-04 at 3 05 52 pm](https://f.cloud.github.com/assets/228733/1272382/46c6cccc-2d2e-11e3-903d-f1097075b44f.png)