Enabled TCP Keep-Alive to Requests

[CastagnaIT]

Check if this PR fulfills these requirements:

• My changes respect the Kodi add-on development rules
• I have read the CONTRIBUTING document.
• I made sure there wasn't another Pull Request opened for the same update/change
• I have successfully tested my changes locally

Types of changes

• New feature (non-breaking change which adds functionality)
• Feature change (non-breaking change which change behaviour of an existing functionality)
• Improvement (non-breaking change which improve functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

From research conducted by @jakermx discovered that Requests module provide Keep-Alive support thanks to urllib3 module,
but the real problem is that the Keep-Alive in the urllib3 module is not enabled by default https://urllib3.readthedocs.io/en/latest/reference/urllib3.connection.html and this is not mentioned in Requests module documentations.

By tracking network activities with Wireshark there is a clear evidence of the lack of TCP keep-alive communications,
and enable it seem definitively resolve the errors:
ConnectionError: ('Connection aborted.', error("(104, 'ECONNRESET')",))
ReadTimeout: HTTPSConnectionPool(host='www.n*****x.com', port=443): Read timed out. (read timeout=None)
Ref issues: #1004, #914

then this (partially) nullifies the workaround of PR #1046 (read below)

unfortunately the embedded python on Kodi 19 for Windows has been compiled without socket.ioctl therefore is unusable,
i have opened an issue xbmc/xbmc#19204 to ask to fix it and (i hope) will be included on Kodi 19.1
The fix has been merged on Kodi nightly

In case of Feature change / Breaking change:

Describe the current behavior

Describe the new behavior

Screenshots (if appropriate):

[jakermx]

nevermind....it is for koi19 based on python3