Improve configurations

Breaking changes

• The configuration interface for livereload and the HMR has changed.
  Please update your configuration and usages accordingly.

Features

• You can now have multiple style processing configurations.
• Style processing configuration is more flexible now.
• Watching of SASS files with sass-graph allows us to rebuild sass only when really needed.
• Disabling of single tools executed by dev or dist can be done by setting the according configuration to null.