Update/optimize images

[UdjinM6]

Should fix win installer and debian packager logos/images.
This also fixes the script for pngs and slightly minimizes the size of few new images used in qt.

[nmarley]

utACK

Would prefer to add to a point release unless a new rebuild is necessary because functionality or security is compromised.

[UdjinM6]

This is needed basically to reduce the number of complains about installer using old logos :) Assuming we are going to prepare "the very final" build anyway due to #2148 bug, I would include this one as well.

[nmarley]

@UdjinM6 If #2148 is a bug which affects usability then it might be a good idea. Just trying to prevent re-building via Gitian, re-verifying results from multiple developers and gitian signatures if possible.