Fix combobox size

Use and install PNG icons instead of ICO, rename P-face to pronterface

 * PNG icons are smaller and there is no advantage in ICO files containing only one resolution
 * It's coomon to name the icon after the app

Update graph.py to 10s/div horizontal scale.

Make temperature graph intervals be 10s as in comments.  Fixes issue https://github.com/kliment/Printrun/issues/491

Don't check for E: in temperature report.

Repetier firmware doesn't have that, but otherwise works.