code completion reduction

[shiffman]

I've been playing around a lot today with PDE X and right now code completion feels a little overwhelming to me. I am not sure exactly how to find the right balance but some thoughts:

• maybe no code completion until you type 3 letters instead of 2?
• we should remove lots of unnecessary classes and only code complete for core Processing API (plus maybe some exceptions). I know we did one round of this but I think we need another. @benfry suggests that you take a look at preferences.txt in the processing repo to see what the default java imports are for Processing.

[Manindra29]

Ideally we should have a key combo to trigger it, and have a more relaxed(or tweakable) letter threshold. Now that the main feature is in a working condition, I can start looking into these aspects.

In the backend, all the jre classes are read. I've already filtered out many unnecessary packages from jre. But this needs further work to be done. Taking only the default imports into account could be a good starting point.