A lot of work toward enabling Stanford and hint visibility experiments:
- Specified levels on which experiments should take place.
- Switched to using ip addresses, rather than user ids, to determine
  experiment options.
A lot of work toward enabling Stanford and hint visibility experiments:
- Specified levels on which experiments should take place.
- Switched to using ip addresses, rather than user ids, to determine
  experiment options.
Added ip_hash field to activity_hints.
Improved tests.
Merge branch 'experiment' of github.com:code-dot-org/dashboard into experiment

Conflicts:
	app/controllers/application_controller.rb
Removed tests duplicated in prior merge.
Minor improvements.
Changed hashing to generate nil for bad/missing ip addresses.
[Fixes #75847736] Normalize block XML by removing blank nodes
Merge pull request #1092 from code-dot-org/experiment

Enabling Stanford and hint visibility experiments
rename pt-br
Merge branch 'finished' of github.com:code-dot-org/dashboard into finished
fix level_test to provide valid xml for program solution, and allow empty tag in xml block formatting
replace bracket with HTML code in Maze editor legend text (fix html parsing warning)
Automatically built
Merge pull request #1108 from code-dot-org/normalize_blockly_xml

[Delivers #75847736] Normalize block XML by removing blank nodes
Merge pull request #1111 from code-dot-org/finished

Deploy to delivered