Adds Section Header and Footer View

# What it Does

Adds the ability to set `headerView` and `footerView` properties on `JMStaticContentTableViewSection` in order to show custom headers and footers in sections. This is particularly useful in the about screens of our apps at @Lickability.

# How to Test

To test this functionality, I simply created `UIView`s with a `backgroundColor` of `cyanColor` and set them as the `headerView` and `footerView` in the Sample application. I didn't check this in because it's ugly and I didn't want to disturb the beautiful Settings.app theme.