Fixed the documentation and completed it a little. Small improvements on the backend code.

Documentation:

- fixed wrong relative links
- added missing relative links (hope these ones are good)
- cleaned and improved a little, added or moved some content

Standard Error:

- renamed the module file containing our own standard error from 'error' to 'stderror'

Editor / Mode manager:

- changed the name of the GUID class to DocumentID
- fix what broke everything: the properties definitions in the schema of the DocumentID class

Code:

- added some descriptions in the schema
- began preparing the class to use a schema at construction

Color:

- added some descriptions
- added serialize and parse methods
- prepared the schema to accept HSV & co. models

Graph visualizer:

- added actions to test standard routes of the backend: GUID identification and shutdown