fixes#1645
- removes server.get('ghost root') as it is only an alias
to config.paths().path, and adds unnecessary indirection
- removes config.theme().path as its just an alias to
config.paths().path, updated all relevant references
- update config.theme.update to only require the api/settings object,
and no longer need the config object
- modify api/settings.edit to call config.theme.update so that
the themeObject is ready for next rendering of template
fixes#1575
- Moves most code that was in ghost.js into ./core/server/index.js
- Creates ./core/server/config/theme.js to hold all theme configurations
(which previously lived on ghost.blogGlobals())
- Removed ghost.server, passing it in as an argument where needed
and allowing middleware to hold onto a reference for lazy use.
