Remove box-shadow and texture to flatten design

* From main header
* From main titles
* Remove text shadow from titles and links
* Remove text shadow from quote icons
Use a border instead of solid background for nav items

Remove increase in size on hover
Add hover color instead.
Flatten the banner

Remove box-shadow form banner and add solid borders to make the
illustion of the banner shape.
Remove the tails from titles at 1200px width
Use site-header and site-footer as classes for header and footer

The selector header {} and footer {} are not robust enough - even
though this is just a personal blog, they should be styled properly
Flatten code snippets by removing inset box-shadow
Flattening in the comments form

Remove text-shadow from comments icon
Remove border, background and padding from allowed tags block
Remove shadows and borders from buttons
Merge branch 'flat-design'

* flat-design:
  Remove shadows and borders from buttons
  Flattening in the comments form
  Flatten code snippets by removing inset box-shadow
  Use site-header and site-footer as classes for header and footer
  Remove the tails from titles at 1200px width
  Flatten the banner
  Use a border instead of solid background for nav items
  Remove box-shadow and texture to flatten design