Added customization options for configuration to allow more styling

[ValentinDenis]

I added a few customization elements that I needed for my project. These are:

• Allowing to add borders (black and not customizable for now) to cells and headers
• Allowing to change header background color (I added a new backgroundView to the headerFooter xib since you can't change backgroundColor of reusableViews, by default it's UIColor.clear)
• Allowing to change text alignement for Header/Footer and data Cells (by default .natural to keep handling RTL languages)

[pavankataria]

Hey, I look forward to checking this out during the weekend! Great work here.

Have you considered adding an example which showcases this work?
Consider adding it in the menu view controller to showcase this work in the mean time.

[ValentinDenis]

I added 3 MenuItems as examples, I hope this will do :)