Make console.log statements conditional; minor refactoring

This pull request is in conjunction with: https://github.com/nens/lizard-nxt/pull/213

PROBLEM
========
There are console.log statements galore within our code base, and this is problematic due to the following points: 

- We shouldn't show clients any debug info which is meant for devs' eyes only.
- It pollutes the code, and henceforth diminishes readability
- It breaks the JS behaviour in certain (old) browsers, including, but possibly not limited to, IE 8-

SOLUTION
=========
make console.log statements conditional, the condition being based on the current environment in which the app runs (::= development | production | ...). 

This value is subsequently (i) written to base.html by Django, (ii) read from that exact same part of the code by the JS (on load from base.html), written to a globally accessible JS variable (window.JS_DEBUG) which can then (iv) be used all over the place to prevent debug info from being printed.

TODO
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nothing, ready for merge