Updated twine structure and comprehensive validation

Major upgrade and improvements to documentation and twine structure.

Documentation was updated to allow for a slightly clearer twine structure (improved key names and a reconciled approach to treatment of files/values for inputs/configuration).

Comprehensive validation of credentials, children and manifests was added, as well as various helper methods and properties based on need in the octue-sdk-python library (which has a number of thorough use cases for the Twine class.

Examples were also added, for use as demonstrators in a development project.