New: test source if set in TEST_DIVA environment variable

build.sh will now trigger different tests depending on the TEST_DIVA env variable. This will be used in Travis CI to have parallel build environments to test source and built files.

Refs #129
New: add separate environments for testing source and build

Refs #129
Fixed: too many Travis CI notifications

Only notifies the channel on a change in build status to avoid spam.
New: specify testURL to unit tests via arguments

We will use this to trigger separate testing of source and built code when calling phantom.js from within the build.sh build script.

Refs #129
Fixed: only diva.min.js should be included in the single.html demo

When running demo/single.html, we should be demoing the minified version only (diva.min.js), not the minified version plus the source (full diva.js). In the minified version, utils.js and all of the plugin js files are included by Closure.
New: html file that includes diva's sources for testing

This HTML file includes diva's sources (as opposed to tests/index.html, which includes the minified code only.) We will run phantom.js using this file whenever we want to test the sources instead of the build code.

Refs #129