Update website for 0.5.0 release

[gak]

TODO

• Include MinGW_build_kit.zip (FrMo/gravit downloads) on the website, linking from http://gravit.slowchop.com/BuildingFromSource/
• Even though there is a link rel for the shortcut icon, many browsers and crawlers specifically want favicon.ico in the root

DONE

• Make sure every reference to Gravit mentions 0.5.0 rather than 0.4.3
• Update git clone links to use https instead of git
• Reorder older downloads by version first, O/S second
• Remove the on-the-fly compiling of the less css, for faster rendering on the client  * Update analytics to track number of downloads and various other metrics  * Make sure Google+ posts are updating on the home page

MOVED

• Split the BuildingFromSource page into 3 sub pages for each operating system or build method #78

[FrMo]

The old website used to have a link to google groups, and an option to register to the mailing list. This is missing in the new version.