Fix EZP-21963: create separate "promise-based" build

JIRA issue: https://jira.ez.no/browse/EZP-21963

Done. 

 * Additionaly, I have created separate page for manual testing of the promise-based version, since it became a non-trival matter to include it into a project, and also as means of "integration testing" for the promise-based version and it's external dependency.
 * Updated readme a bit
 * I had to reconfigure the unit tests, since the Q dependency is not mentioned in `define` call now.
I'm not 100% sure, that ` window.Q = require("../../node_modules/q/q");` is a nice fix, but it works and looks quite nice to me :) @jakobwesthoff, your opinion is welcome here. May be I've even chosen a wrong way to get rid of "manifested" Q dependency?