Update documentation with respect to changes in core and hydrus

[sameshl]

A lot of new changes in hydra-python-core and the hydrus server have not been incorporated in the docs yet. This really confuses a new user when he is going through the docs like developing with hydrus.

Some of the major changes required immediately that I can think from the back of my mind are:

• read-only and write-only properties are now readable and writeable. (Read here)
• Status Codes now can't be defined in python dict objects. They need to be defined using either HydraStatus or HydraError classes. (related to here)

I will keep appending more changes required to this issue.

[ayan-biswas0412]

@sameshl can I work in this issue ? Can you elaborate me more on the topic , the project seems very interesting and I want to work for it