Make tooltip behavior consistent with the notebook

[anntzer]

Currently, the qtconsole still shows tooltips upon opening a parenthesis, whereas the notebook has switched (for reasonable reasons) to requiring shift-tab for triggering the tooltip (jupyter/notebook#167) -- a shortcut that does not exist with the qtconsole. It would be nice if the behavior could be made consistent across frontends. (Also, is there a way to display very long tooltips in the qtconsole? It seems that they just get truncated with an unhelpful "Documentation continues...")