Made the tab bar gradient colours, and the border colour, configurable.
Merge pull request #3 from mz2/master

Gradient start / end color, and border color, made a public property and thus configurable.
Added some Xcode user data to .gitignore
Only draw the gradient bar if a color is set for it. Only draw the bottom border if a color is set for it.
Merge pull request #5 from mz2/master

Make the tab bar background drawing and border drawing optional