* FEATURE: introduces minimum trust level for polls
This commit makes `poll_enabled` less misleading and introduces `poll_minimum_trust_level_to_create`. If poll are enabled they will always be cooked, and if you have the required trust level you can create polls. As a side effect, it also fixes a bug where rebaking a post created by staff member when `poll_enabled=false` would end up not cooking it.
It also adds more tests to ensure settings are respected.
* admins should be whitelisted
* checks for admin in post validation
* test for >= instead of == trust level
* Add rubocop linting to docker:test rake task
* Add eslint JS listing to plugin files, and add SKIP_LINT variable
* Fix failing ‘polls’ plugin eslint
Using eslint-disable-line, as is done in core qunit tests such as `acceptance/group-logs-test.js.es6`
* Add plugin test eslint to travis config
* Merge some eslint lines
