Move javascript test helpers to IntegrationTest

Test helpers are useful for both IntegrationTest and
JavascriptIntegrationTest classes.

* Add helper to check whether test is using javascript
* Switch action within save_edition based on this (default driver has
no trigger action)
Test editing of business support with & without js
Allow saving of business support without js

When validating business support editions it expects areas to be an
array. Submitting without JS gives a comma separated string.

* If a string is submitted, coerce it into an array
Simplify business support areas js

Now non-js submission works we can avoid using a hidden input for the
select2.

* Use the text area for the select2 field
* Submit data as a comma separated string rather than a rails array