Update mainpage.html

updated to match the new installation protocol (no need to install and/or locate StochKit anymore).
Merge branch 'develop' of https://github.com/StochSS/stochss into develop
Simplified mainpage
fixed a couple of typos ...
Installer now installs git as well
Allow user to cancel these scripts easy-like
Merge remote-tracking branch 'upstream/develop'
Updated ubuntu install script to correctly check for installed packages