Proof of concept new style specs

Hi again all,

Here's a little proof of concept for how I would like to see style specs working. The big idea here is to
* Get rid of `all_the_styles` and all the `behaves like` things that were added [here](https://github.com/shoes/shoes4/blob/master/spec/shoes/shared_examples/style.rb).
* Test the 5 setter methods and 2 getter methods for styles described [here](https://github.com/shoes/shoes4/pull/683#issuecomment-43389269). In this PR that looks like this:
  * **Setters**
    - **During creation of element** - tested in element tests no changes in this PR
    - **Via element-setter** - newly added tests iterate through each supported style and check that the element responds to a setter and that `update_style` gets called.
    - **Via style method** - small modifications to existing tests for this
    - **Element-level setting** - newly added tests (discussion in line)
    - **App-level setting** - tested on app no edits
  * **Getters**
    - **`style`** - small modifications to existing tests
    - **method** - newly added tests iterate through each supported style and check that the element responds to the getter and that `update_style` does not get called

* I hope that this will generate some discussion to make sure everything is getting tested that we can think of (well . . . or that we can think of how to test) before putting #711 to rest.

* I've only applied these tests to arc (and commented them out temporarily on the others) to keep things simple, but I'll add `it_behaves_like "object with style"` to all the elements from #711 before this is submitted.

Sound good?
I'm almost always in the favor of extracting small intention revealing methods. Here, however, it seems quite long and the doesn't have default part is kinda... irritating because the app level defaults are also defaults to me.

But yeah, extracting that part seems good.