It used to validate the post from the perspective of the user who
created the post. That did not work well when an admin attempted to
add a poll to a post created by a user who cannot create posts because
it said the user cannot create polls.
The problem was that it used post.user for the validation process
instead of post.acting_user.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
* 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
