Add 'guess import' script and enhance util

New pair of scripts: one to build an index of Java imports in each project you open, and another that lets you search the index to generate import statements.

The idea is that when you're writing a new source file, and you need to import classes, you've probably imported the same things before somewhere else. So, by doing a very fast search of what you've used before, we can offer a usually-good-enough imitation of an autocomplete feature provided by heavyweight IDEs like Eclipse and Intellij.

Could probably be adapted to other languages by adjusting the pattern-matching (eg don't require dots for Python imports).