Hy 1142 rectangle class

Spawned from https://github.com/WebFilings/wf-js-viewer/pull/167


**Jira Ticket:** [HY-1142](https://jira.webfilings.com/browse/HY-1142)

## Problem
Want a simple rectangle class to support hit testing forbidden areas.

## Solution
Created a new Rectangle class that includes a single method to determine if a point is inside the rectangle.

## How to QA/+10
1. CI Build Passes
1. Check out the `HY-1142_rectangle_class` branch
1. Run `./init.sh && grunt qa`
1. Confirm lint and unit tests pass

# Code Review             
@timmccall-wf @lancefisher-wf @robbecker-wf @patkujawa-wf @georgelesica-wf 
Oh, and by not prefixing these props with an underscore, we're making an implicit public API. Personally, I'm fine with that.