Renamed exiting Splitter to DefaultSplitter and added trait Splitter

Added:
- Added trait Splitter, to bring the splitter in line with the other
parts of the system

Updated:

Fixed:
- Renamed package core under test to manager
- Renamed exiting Splitter to DefaultSplitter

Removed:
Merge branch 'rename-splitter' into development
Bumped version number to 0.5.3
Merge branch 'bump-version-number' into development
Merge branch 'development'