Update and Use Latest Octicons

[Hirse]

This builds on #1223 but with the latest version of Octicons.
With that version the icons are used as SVG instead of fonts.
(Credit to @exsilium for the work in exsilium#4.)

• All changes from Use consistent icons in dropdown #1223
• Use latest version of Octicons
• Changed icons
  • Use verified instead of key for PGP signatures (as GitHub does)
  • Use skip instead of i to add files to ignore (avoid confusion from i being used for "information")
  • Use globe instead of broadcast for "remote" consistently (as it was already the case for tags)
• Switch + and x to octicons consistently (from glyphicons and unicode)
• Use octicons for refresh button and align design with other buttons
• Use actual <button> for ignore and discard files in staging
• Fix all semicolon and quote mark lint violations in changed files

[campersau]

No more icon font 👍