Make Optimizely per-page opt-in. Bug 1107952.

- Update docs to reflect Waffle configuration.
Switch to the new Docker-based Travis CI builds.
Update legal-dos to latest master.

Changes:

78996df Merge pull request #268 from GeoffPiperMZ/patch-9
d5e8809 Update en-US.md
8442c99 Clarifications
d99a09f Clarify conversation URLs & direct calls
c6ec83e Change to branding term
ad8cfa2 Clarifications to ToS
a87d1aa Clarifications
7e3dc14 more clarifications in response to governance thread
95ae568 Clarifications in response to governance thread
Fix Bug 1103396 - Move Thunderbird start page to bedrock and make it localizable
Merge pull request #2585 from jpetto/bug-1107952-optimizely-opt-in

Make Optimizely per-page opt-in. Bug 1107952.
Merge pull request #2594 from pmclanahan/try-travis-docker

Switch to the new Docker-based Travis CI builds.
Merge pull request #2600 from pmclanahan/update-legal-docs

Update legal-dos to latest master.
Merge pull request #2539 from kyoshino/bug-1103396-thunderbird-start

Fix Bug 1103396 - Move Thunderbird start page to bedrock and make it localizable