* SINGLE_PROCESS_MODE environment variable takes precedence over
  application.yml setting
* SINGLE_PROCESS environment variable takes precedence over
  SINGLE_PROCESS_MODE environment variable to be backward compatible

prefer config/script_server.yml over config/script_server_config.yml until we remove the support for the later completly

* clean up unneeded stuff
* added moar config checks

Switching to settingslogic to manage our configuration. THE FILE FORMAT HAS CHANGED. OLD APP.YML AND APP_CONFIG.YML FILES WILL NOT WORK ANYMORE.
Two important differences:
1. The app only looks in one file for settings: config/application.yml. If you want to override something, do it in that file. It is gitignore'd. If config/application.yml does not exist, or exists but is in the old format, you'll get a nice friendly set of instructions on how to convert your old file.
2. script/server settings are no longer in application.yml. They have their own settings file - copy config/script_server_config.yml.example to config/script_server_config.yml. This is also gitignore'd. script/server will print a message and exit if that file doesn't exist.

rename config/app_config.yml to config/app.yml in accordance to The Redundant Rendundacy Act of 2011

eliminate config/server.sh; use config/app_config.yml.example as base for configuration, config/app_config.yml is now just an overider. This way we can add new configuration options without checking in the application if it's set and the user has to update his app_config.yml only when he want to change something

replaced SOCKET_PORT in config/server.sh with the setting from config/app_config.yml; respect single_process_mode setting in app_config.yml in script/server

Updated the server script to support Redis when it has been installed via MacPorts. Also, fixed an echo error with it not being displayed correctly.

When using sub-uri, create a symlink in public/ making the assets
available at the sub-uri. Modify environment.rb so that asset paths
refers to this sub-uri path. Closes http://bugs.joindiaspora.com/issues/391
and http://bugs.joindiaspora.com/issues/737 when application mounted
on suburi (i. e., prev patch)