Use Application keyWindow when displaying from a BarButtonItem

The the ViewController happens to be a TableViewController then when
presenting from a BarButtonItem the topViewController was being
selected at the containerWindow. The problem with this in the case of a
TableViewController is that the PopTip view would scroll with the
table.

Suggested solution here is to use the Applications keyWindow in this
case.
Add hasGradient property
Change property name to hasGradientBackground and set default value to YES
Merge pull request #42 from sodbileg/gradient

Add hasGradientBackground property.
Tested hasGradientBackground property in demo app.
Version: 1.3.0
Updated copyright message.
Ramped up compiler warnings. Minimum deployment target is now 5.0.
Version: 2.0a1
Converted to Objective-C ARC.
Updated README about ARC.
Delegate method is not optional.
Added a Retina4 launch image.
Set the window's root view controller.
Removed explicit synthesizing. Moved ivars to class extension.
Enabled -Weverything and cleaned up the code.
Re-enabled landscape orientation for iPhone demo.
Merge pull request #40 from antokne/master

Use Application keyWindow when presenting from a BarButtonItem
Configured project to use spaces instead of tabs.
made cornerRadius public
added comment with example in demo