Changed back button to home, always scroll to the top

when the page changes
Quieter error handling when a media type is not registered
Plays nicer with save

Calculating whether content is dirty is simpler
If a resource does not have a title fall back to displaying its path
Handles navigation tree with links to internal elements
Resolve relative links in nav doc so models can be looked up
Removed log file
Large refactoring and got richer menus

With quick buttons to load other EPUBs stored on Github!
Merge branch 'dev' into epub
Merge branch 'epub' into gh-book