Some minor editor improvements.

[iphydf]

• Add source formatting on the server. Not ideal, because it causes a full reload. Ideally, we would send edits like firepad itself does.
• Enable code folding (braces and markdown).
• Load all toxcore sources by default.
• Only build //c-toxcore/... for now.
• Add better search box: Ctrl-F / Cmd-F.
• Highlight trailing whitespace.
• Search and highlight current selection in viewport.
• Add "jump to line" command: Alt-G (doesn't work on Mac).

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This change is