Make auto-completion behaviour configurable

[imagejan]

I suggest introducing an option to trigger the auto-completion by Shift+Space (as it is in Eclipse) instead of having it always try to auto-complete anything you type.

The current auto-completion behavior can get quite inhibitory when you want to type something, and by the end of the line, when hitting Enter you end up with complete nonsense, e.g. because the auto-completion replaced your script parameter name by an entire macro snippet.
In its current state, the auto-completion (in particular the one for Groovy shipped with the CLIJ update sites, but that's another story...) makes me slower rather than quicker in setting up a script :-/

I think we discussed it in person some time ago, @haesleinhuepf, but there's no issue tracking it yet, as far as I can tell.