fix v2 issues

[grmbyrn]

• change from using window in TableOfContents to using IntersectionObserver
• fielename prop in component should be optional #49
• Normal links don't have any special style #48
• Ask the designer how to implement a link inside a key feature card #42
• Blog post tags style is not the same as the design #38
• Ask the designer how to implement html lists #37
• Font size for table of contents is not as the design #31
• Ask the designer how to implement share links in blog posts #29
• Related Post section does not look like the standard blog post list #27
• Top menu padding is not the same as the design #26
• Key features list width should be 100% #6

[josecelano]

ACK cbe642e5371d4737d976cec1f20f0d9edb729e45