Merge pull request #285 from bentrm/travis

Remove CasperJS from the GeoExt repository only installing it via NPM if needed.
Add example to API docs of `ignore`-config option.
Merge pull request #287 from marcjansen/better-ignore-doc

Add example to API docs of `ignore`-config option.
Add new component GeoExt.container.Overview
Add tests for component GeoExt.container.Overview
Add examples for usage of GeoExt.container.Overview
Merge pull request #288 from bentrm/overview

Simple overview container
Run headless test suite on engine SlimerJS  (Gecko) as well.
Install SlimerJS before executing headless tests.
Install SlimerJS before executing headless tests.