Harmonize nexus-python-sdk modules (e.g. docstrings)

This is feedback provided after a first usage of the nexus-python-sdk and its documentation to perform basic operations in a Nexus V1 deployment.

Regarding harmonisation, the following notes were taken:

* Standardise the wording of docstrings (e.g. in the docstring of returns: `**"Returns:** All the details of this organization, as a dictionary"` vs. `**"Returns:** The payload from the Nexus API as a dictionary. This contains the Nexus metadata of the organization"`
* Remove probabilistic wordings, such as `This is most likely the returned value of organisation.get(…)`
* Finish each sentence with a full stop
* Make difference between `nexussdk.projects.deprecate` and `nexussdk.projects.deprecate_2` explicit
* Include a link to the source code in the documentation
* Correct typo in `projects.fetch`; `Fetch a project and all its details. Note: This does not give the list of resources. To get that, use the resource package` should be `(...) resources package`