Add documentation based on readthedocs

[dachengx]

Examples, tutorials, usage of:

1. Parameters
2. BlueiceDataGenerator
3. StatisticalModel, particularly the degree of freedom of required attributes and functions, like the type of data
4. BlueiceExtendedModel

and required format of statistical model and runner configuration:

1. what keys are needed
2. rate and shape parameters
3. parameter of interest

We now have BlueiceExtendedModel which is designed based on blueice. It will be beneficial to clearly describe the structure of BlueiceExtendedModel instance, like its attributes and attributes of its attributes. I believe some of them should be in blueices's documentation, but also good to first implement here.

[hammannr]

I think one of the very important pieces of information that we should document well is how to properly write a config file for the BlueiceExtendedModel and what options you have.