Should add a find command

[Noam Yorav-Raphael]

ctrl-f should open a simple find text box.

I think that google chrome interface is nice - just a textbox and up and down buttons. ctrl-f opens. In chrome, ctrl-g searches forward and ctrl-shift-g backward. We should start from the end. Perhaps ctrl-f should also work (or only work, and discard ctrl-g?)

The best place to put the search box: instead of the status bar.

It should search both the history and the code box.

Highlighting matches would be nice. Searching can be done by TextIter.backward_search(). To make things fast, we should only highlight, say 20 matches.