Rename regionManager.spec.js tests to map to public interface

The regionManager tests actually have pretty good coverage of the public interface, but it's tough to tell by reading the descriptions. This refactor just changes the names of the descriptions so they refer to the public methods:

[old](https://github.com/jasonLaster/backbone.marionette/blob/cbdd6decbab86e82eba24eb63fe58bb187fc4372/spec/javascripts/regionManager.spec.js)  --- [new](https://github.com/jasonLaster/backbone.marionette/blob/9496b4fcfd05a4118257b0a1275221b1171639bd/spec/javascripts/regionManager.spec.js)

Here's a pretty picture to show what I mean.
![](http://f.cl.ly/items/3C1O1n291y3f1m3Q0X1w/Image%202014-04-02%20at%208.31.10%20PM.png)