Added documentation for content processor rainpress
Added content_processor.rainpress to the overview listing
Spelling fix
Configured the website.base_url option
Updated base CSS to only include necessary bootstrap components
Some small updates to the main template
Removed separate bootstrap.scss and moved everything into design.scss
Updated the main pages (home, installation, ...)

* Better, clearer landing page
Link to API documentation for each extension
Added link to Node API doc in content_processor.fragments documentation
Added reference documentation for the Webgen Page Format
Added global link def for Webgen Page Format reference page
Fixed links to meta information key references