Source state improvements

General improvements to the source.sls state.

- Added 'silence_compiler' option which will cause all stdout from source build/install to be suppressed (logged to a file, in case you want to see it later).  stderr is also logged to file, but if there is an error then stderr is copied to Salt so it comes back with the highstate payload.
- Now restart nginx service instead of reload.  Reload, while nice on config updates, doesn't have the required effect when you upgrade nginx.  If we can reload on config update and restart on code upgrade, that would be great.  For now we just always restart.
- Moved use_upstart and use_sysvinit default values into map.jinja.  Source install now using default user/group names defined in map.jinja.  Moved more default definitions from source.sls into map.jinja.
- Added optional ability to disable creation of /etc/nginx/sites-(available|enabled)
- Removed duplicate service enabling code.  "service -> enable: True" does this already, you don't need to explicitly call update-rc.d