Merge pull request #247 from Hill30/scroller

Rename scroll directives to 'uiScroll' and 'uiScrollViewport'
Rename residual ng-scroll -> ui-scroll instances

ng-scroll was recently renamed to ui-scroll, but there were places where the
rename was missed (crucially, the readme!).
Merge pull request #249 from tlvince/bug/scroll-readme

Rename residual ng-scroll -> ui-scroll instances