(#1704, #1716, #1722) Decreased blog post width, changed sidebars depending on page, fixed sidebars.

#1704 - I've decreased the width on blog posts by about 200 pixels.

#1716, #1722 - api.html sidebar has only API links, while the other pages have nav links only in the sidebar. The sidebar is fixed only when the page has width of at least 770px and height of 475px. I also added the links "Events" and "Plugins" to the API sidebar and removed "List of Databases" from the API sidebar since that section didn't seem to exist.

Small issue: after generating the css using less, there are two instances of .affix present because .affix is in bootstrap's utilities.less. That one needs to be removed before the css is used in the website.