Add cljs tests

[annapawlicka]

• Add test cljs build
• Update phantom.js test helpers
• Update cljs and om
• Update project.clj to use lein 2.5.0, new cljsbuild and new lein clean command
• Change structure of the project to look like this: |-- project.clj |-- src | |-- clj | |-- cljs |-- test | |-- clj | |-- cljs |-- resources | ...
• Update README.md with new build and test commands
• Update .travis.yml to run cljs tests

[otfrom]

:shipit: