Psiturk

Added
- added backwards compatibility for class `InvalidUsage` exception in
experiment_errors.py, for custom.py files generated by old version of psiturk.
This was previously throwing an exception in versions 3.0.0 – 3.0.5 (479)
Fixed
- fix bonus_message config.get section reference (3219016)
- fix another reference to a config section name that doesn't exist, apparently
the unit tests are horrible

Fixed
- Fixed backwards compatibility for translating ON_HEROKU=1 to ON_CLOUD=1

Fixed
- fix shell's error during hit_create that prevented ad url from showing.
- fix shell's messaging about invalid aws credentials

Fixed
- Changed default ad url port to 443 instead of 80

Changed
The currently-undocumented `psiturk-heroku-config` command no longer attaches a postgresql addon by default.
I'm calling this just a bugfix because (1) the docs assume that it _doesn't_ attach the psql database, and
(2) that command isn't even documented anyway. Will version-feature-bump when this feature is better
thought through.

Fixed & Changed
- fixed an inconsistency between shell usage of "allowlist-qualification-ids" and
and config file calling the same "require_quals", same for "blocklist" and "block_quals". Also, documentation incorrectly described the config file accepting "allowlist_qualification_ids", while it only actually accepted "require_quals." Standardized on "require" and "block" throughout. Maintained backwards compatibility except in shell usage since docopt
doesn't seem to allow it in the way it parses the usage string, but no way
am I going to bump to 4.0.0 just because of that!