Tweaked skin.js for "flat" skin window sizes

[linuxsense]

I really like the new 'flat' skin but on my systems the window popups were not quite right. The width on most was fine but the height was always too small. These changes might not be right for your system but with Chrome on Linux it sorts everything out quite nicely. Just place the modified 'skin.js' into the 'js' dir for the skin. On my system its in '/usr/local/share/zoneminder/www/skins/flat/js/'.

https://dl.dropboxusercontent.com/u/6511963/skin.js