Added MKProgressView

[rz-robsn]

Hi,

I have created an indeterminate ProgressView.

• I inspired myself from the material circular progress component
• The progress line color and line width can be changed. Leaving the default values will make the progress appearance close to the one shown on the link above.
• I have added an example of the progress view in the BarButtonItemViewController on the storyboard.
• The MKProgressView is backed by a custom CALayer (called MKProgressLayer). This layer defines a few custom properties that are animated and used in the drawInContext() method.

If you have any questions, let me know !