Added Several Things

Changed "End" to "Play" in index_content.html to display them right.
Added Browser Pictures & added them into a better Message in IE.
Added "View on GitHub".
Issue #6

Changed download button to directly link to
"http://jenkins.movingblocks.net/job/Terasology/lastSuccessfulBuild/artifact/build/distributions/Terasology.zip",
and the download_content.html is useless when it's directly linking
there.
Adding Ajax in "develop_content.html"
Fixed the AJAX/non-AJAX links :D
Merge pull request #1 from MiJyn/master

Fix AJAX/non-AJAX
Changed Buttons
Added GitHub Ribbon
Changing IE Message
Fixed Broken Link
Merge #15 from @NowNewStart and @MiJyn for assorted changes
Bunch of tweaks, cleanup, couple extra backgrounds, etc. This and the previous PR together ...
- completes #13 - Github branding
- completes #12 - Initial background addition & compression
- completes #11 - End button gone, Play button added for applet
- completes #10 - Develop menu with links
- completes #6 - Download button