Backports from master:
- Removed logging configuration from Quick Tutorial ini files except for scaffolding- and logging-related chapters to avoid needing to explain it too early.
- clean up line spacing in quick_tutorial/debugtoolbar.rst
- improve wording and grammar in debugtoolbar.rst, requirements.rst, json.rst
Backport from master:
- Clarify a previously-implied detail of the ``ISession.invalidate`` API documentation.
Backports from master:
- add links to issue tracker for items previously released under 1.5.1
- document other backports in this PR
Merge pull request #1440 from stevepiercy/1.5-branch

backports from master to 1.5 branch