Updated font icon set with a bunch of new cool icons
Made Sidebar allow for custom icons as specified in tag.icon
Updated compiled CSS... we really should make this not included in repo
Test script for message header parsing work
 Enhanced plugin loading for external plugins.

 New manifest.json features are:
 - startup and shutdown hooks
 - register mailboxes
 - pass config to mailbox parse_path
 - Added usage examples to demos plugin

 Necessary enhancements for external LEAP plugin.