Create bouncesHorizontally property

This adds the ability for the developer to customize the RESideMenu further with the addition of the **bouncesHorizontally** property. It works similarly to UIScrollView's **alwaysBounceHorizontal** property. It fixes a problem in which if the **menuViewController.view** is not 100% transparent, it would look weird. To illustrate it, let us take a look at a few screenshots.

1. In the image below, the menu is visible, but no dragging action is happening.
![menu_visible](https://f.cloud.github.com/assets/650942/1770940/a11eca9e-67a3-11e3-9081-bba7ed252b98.png)

2. If we drag it further to the right, the bounce effect causes a weird effect, which may not be what the developer wanted.
![menu_bounce](https://f.cloud.github.com/assets/650942/1770955/28eedc70-67a4-11e3-86eb-955a4d430369.png)

In conclusion, this property helps alleviate that problem by not allowing the scaling and translation animations of the **menuViewController** and **contentViewController** go beyond the maximum threshold.