Assorted changes leading toward dqsegdb 2.0.0

Created by: robertbruntz

Creating a PR to run CI on the changes in the code.

• This version drops support for Python 2. Binary (scripts) run in Python 3 in any environment.
• Made numerous updates to outdated email addresses and URLs, fixes to typos in documentation and comments, and improvements to documentation and comments in several places
• Fixes to code to address several issues ( https://github.com/ligovirgo/dqsegdb/issues ):
  • #48 (closed), #83 (closed) - dqsegdbCheckVersion was broken due to a typo and an issue in apicalls.py
  • #63 (closed) - fixed issue with importing reduce in ligolw_segments_from_cats_dqsegdb
• Numerous other fixes in progress, but I'd like to see what CI thinks about what's been done so far [it worked]

Later notes: Other changes and fixes in this (large) PR:

• P3 fix to urifunctions.py, to deal with TypeError: POST data should be bytes... error.
• Ran 2to3 and made almost all recommended changes
• Fixed 2 string/bytes issues in urifunctions.py from P2 to P3 conversion (search for 'P3 fix').
• Upgraded Versioneer to 0.21 and ran it, to get date as an output
• Changed executables (in bin dir) from using glue.git_version to Versioneer (get_versions()) for version info. This resolves https://github.com/ligovirgo/dqsegdb/issues/11