Add case-sensitive paths plugin

[Calvinp]

This adds the case-sensitive paths plugin Singularity UI - thus preventing the issue where builds succeed locally but not in Jenkins because the OSX filesystem is case-insensitive.
Now it'll fail locally with this error:

ERROR in ./app/components/tasks/TasksPage.jsx
Module not found: Error: [CaseSensitivePathsPlugin] `/Users/cpomerantz/repos/Singularity/SingularityUI/app/rootcomponent.jsx` does not match the corresponding path on disk `rootComponent.jsx`.
 @ ./app/components/tasks/TasksPage.jsx 17:21-51

cc @tpetr @wolfd @kwm4385

[tpetr]

LGTM