Always take the user to a new window when clicking off site links

Original caused GitHub contributor credits screen to open in the active
page of the ElkArte site. That usually irritates most users. So, now
they get a new window to view the contributor list in.
More Windows to open for off site links

Apparently this is bothering me.  :)
Well ... even more windows to open on a click

This has become an OCD moment for me.  :)
Dress up Modify Themes/Copy a template ...

Besocial and Light did not match in appearance in the Copy a template
section. The light was really poor looking. One had lines one did not,
one had borders and one did not. Now they can match.
Update admin_besocial.css
Update admin_light.css
Attempting consistent background in Theme Management

Changed 3 windowbg to windowbg2, this fixes inconsistent background in
Member Options and Modify Themes. Added windowbg and windowbg2 to css
file. This helps to bring both variants into a more consistent look.
Stay at home ... but look out the window

Changes in the Support and Credits area.  User stays at their site on
one window while they look at the support site on another window.
Removed one instance of double slashes at line 119. They did not seem to
serve a purpose.
Update admin_light.css

I am an idiot ... left out a bg
Update Install.english.php
Merge pull request #1585 from Aggelos777/master

Always take the user to a new window when clicking off site links.