Issue#287: Refactor GeoNode API client module and drop legacy support

[Gpetrak]

This PR refactors the GeoNode API client module and drops the legacy support according to the issue: #287

[giohappy]

@Gpetrak I would implement a more robust and complient method to check if a version is supported. Just comparing the major version with a list of numbers is a bit simplistic.
I suggest to implement a method (e.g. validate_version()) to be used everywhere the version check is required, and compare the version with PEP440 semantics.

The plugin already contains a stripped version of packaging that can be used to parse and compare versions.

For example:

from vendor.packaging.version import Version

v332 = Version("3.3.2post1")
v442 = Version("4.4.2")
v500 = Version("5.0.0b0")
v332 < v442 < v500 # returns True

A check for a valid version should compare a min / max version

[Gpetrak]

Thank you @giohappy . I just pushed a new commit regarding your recommendation.