Pixel.gif to pixel.png

Change pixel.gif to pixel.png + template changes
Template version 1800->1801

Change template version from 1800 to 1801
Replace <img> tag - part 1

Replace <img> tag in forumdisplay_announcement_rating +
private_messagebit_icon
Replace <img> tag in member_profile template

Replace <img> tag in member_profile template
Replace <img> tag in private_archive_html_message

Replace <img> tag in private_archive_html_message
Typo in forumdisplay_announcement_rating
Merge pull request #1510 from Cu8eR/MyBB_feature_pixel.gif

Fixes #1509 - Pixel.gif to pixel.png