Fix ipython prompts: don't focus on input received

[jdanbrown]

IPython's python-prompt-toolkit asks for a "cursor position report" on every prompt, which looks like input to atom-xterm and causes it to steal focus from other panes. Example:

• Run ipython in xterm pane
• Run some slow-ish python computation
• Switch to editor pane
• Sometime later, while you're editing, the computation finishes and steals focus back over to ipython

Here's some rough code pointers in python-prompt-toolkit, for reference:

• https://github.com/jonathanslenders/python-prompt-toolkit/blob/4476b3c/prompt_toolkit/renderer.py#L357
• https://github.com/jonathanslenders/python-prompt-toolkit/blob/4476b3c/prompt_toolkit/terminal/vt100_output.py#L626
• https://github.com/jonathanslenders/python-prompt-toolkit/blob/4476b3c/prompt_toolkit/key_binding/bindings/basic.py#L204
• And a little discussion: https://github.com/ipython/ipython/issues/10416

The fix here is just to not .focus() when input is received. This assumes:

• If the user wants focus on the term pane then they already have it in focus
• If the user doesn't have the term pane in focus then they don't want that to change