grunt: concat and minify our JavaScript files (#157, #163)

Loading the index page of the 0.0.1 release triggers 23 requests for
1.6 MB of data. That took about 2.5 seconds when connecting from my
machine to zebra.zerovm.org.

Concatenating our own JavaScript files brings the number of requests
down to 16. The amount of data is unchanged since our files small. The
time to load goes down a little (in the 50-200 milliseconds range).
grunt: add e2e-build task (#164)

This task will build the project and run Protractor on the minified
sources. This will be useful to ensure that our builds actually work.
travis: run e2e-build task (fixes #164)
grunt: let build.dir denote full build dir path
grunt: leave .tmp directory around after build

This might come in handy if the concatenated files need inspecting.
grunt: minimize third-party Bower components (#157, #163)

This brings the number of requests down to 8 (from 16) when loading
the root page. The size went from 1.6 MB to 0.5 MB.

The page loads noticeably faster now: before, it took about 2.7
seconds on my machine, the time is now around 2.0 seconds.
grunt: minify CSS using cssmin

The number of requests to load the index page is now 7, compared to 8
before.
readme: mention closed issue for the next version
Merge pull request #165 from mgeisler/grunt-usemin

Minify JavaScript and CSS files in build