Added ShowcaseView.ConfigOptions for the ShowcaseViews class

You can now set a ConfigOptions object for each ShowcaseView which is added to a ShowcaseViews object.
During the implementation I fixed some problems with ConfigOptions#fadeInDuration. (https://github.com/nikwen/ShowcaseView/commit/8ce29611ced09c16660ceb81628ea48625c2579b)

Thanks to gravis502 for testing (http://forum.xda-developers.com/showthread.php?p=46295144#post46295144).