add NTRIP client functionality

[semuadmin]

PyGPSClient Pull Request Template

Description

Add beta NTRIP client functionality to v1.1.9. New NTRIP client configuration dialog which allows user to connect to specified NTRIP caster, retrieve sourcetable, select mountpoint, receive RTCM3 correction messages and upload NMEA GGA sentences at selected intervals. Enhancements to app, nmea handler and ubx handler to retain latest navigation readings in global settings dictionary.

Fixes # (issue)

Testing

Please test all changes, however trivial, against the supplied unittest suite tests/test_*.py e.g. by executing the tests/testsuite.py module or using your IDE's native Python unittest integration facilities. Please describe any test cases you have amended or added to this suite to maintain >= 99% code coverage.

• Tested against variety of public NTRIP servers and u-blox GNSS devices.

Checklist:

• My code follows the style guidelines of this project (see CONTRIBUTING.MD).
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• (if appropriate) I have added test cases to the tests/test_*.py unittest suite to maintain >= 99% code coverage.
• I have tested my code against the full tests/test_*.py unittest suite.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I understand and acknowledge that the code will be published under a BSD 3-Clause license.

[semudev2]

Looks fine. Same socket engine as pyrtcm ntripclient.py example which was simple and solid.