Keep AngularUI tab content wired to scope

Fixes Issue #28.

Tab content that is actively tied to scope will now remain active instead of being disconnected from its scope.

Add touch swipe support

• Fix Issue #44: add touch swipe support
• Enhance build process: add header to dist files during build

Restructure; use gulp; add e2e tests

• Break the project into multiple files to make it more maintainable
• Add gulp for development and testing
• Add e2e tests (just basic tests right now--will add more)
• Incorporate changes from PR #41

Breaking Change

The directive files, scrolling-tabs.js and scrolling-tabs.css, have been moved from the project root into <root>/dist/.