Avoid "console" errors in browsers that lack a console

In version 5.5.6 there are many instances of `console.warn(..)` and `console.error(..)`.
This can be problematic in browsers that don't support the `console` object like IE11: an "undefined object" error will be thrown potentially breaking the jsoneditor integration.

Before trying to log to the console I suggest checking for the existence of the `console` object.

Another option would be something like the following script by HTML5Boilderplate.com: https://github.com/h5bp/html5-boilerplate/blob/master/dist/js/plugins.js (it might be a bit too intrusive in the context of an JSON editor though).