BearRunner: Better variable name
coalib: Add default_coafile
settings: Add SectionManager

This adds a Manager object which takes care of all the section stuff,
namely:

- Reading all settings in sections from
    - Default config
    - CLI
    - Configuration file
- Collecting all the bears
- Filling up all needed settings
- Write back the new sections to the configuration file if needed
- Give all information back to caller
SectionManager: Add test