Fix crash on Android 2.3 caused by unsupported APIs.
"This HeaderTransformer is designed to run on SDK 14+. If using ActionBarSherlock or ActionBarCompat you should use the appropriate provided extra."

Changed imports:
uk.co.senab.actionbarpulltorefresh.library.PullToRefreshLayout to
uk.co.senab.actionbarpulltorefresh.extras.actionbarsherlock.PullToRefreshLayout

Thanks:
https://github.com/chrisbanes/ActionBar-PullToRefresh/issues/114

fixes #49
Merge branch 'development'