rose_arch: support source edit

Allow user to specify a command to edit the source.
rose config: add synopsis for top level option

Describe default behaviour. Remove unnecessary description that is already
covered by the synopsis.
rose bush: add host name to brand

Also add favicon to all HTML pages.
Merge pull request #960 from matthewrmshin/rose_arch.source-edit-format

rose_arch: support source edit
Merge pull request #961 from matthewrmshin/doc.rose-config

rose config: add synopsis for top level option
Merge pull request #964 from matthewrmshin/rose-bush.brand

rose bush: add host name to brand