Refactor how model visibility works in index actions:
* Call `visible` in the controller instead of in model `search`
methods. This decouples model visibility from model searching.
* Explicitly pass CurrentUser when calling `visible`. This reduces
hidden dependencies on the current user inside models.
* Standardize on calling the method `visible`. In some places it was
called `permitted` instead.
* Add a `visible` base method to ApplicationModel.
- The only string works much the same as before with its comma separation
-- Nested includes are indicated with square brackets "[ ]"
-- The nested include is the value immediately preceding the square brackets
-- The only string is the comma separated string inside those brackets
- Default includes are split between format types when necessary
-- This prevents unnecessary includes from being added on page load
- Available includes are those items which are allowed to be accessible to the user
-- Some aren't because they are sensitive, such as the creator of a flag
-- Some aren't because the number of associated items is too large
- The amount of times the same model can be included to prevent recursions
-- One exception is the root model may include the same model once
--- e.g. the user model can include the inviter which is also the user model
-- Another exception is if the include is a has_many association
--- e.g. artist urls can include the artist, and then artist urls again
The belongs_to_creator macro was used to initialize the creator_id field
to the CurrentUser. This made tests complicated because it meant you had
to create and set the current user every time you wanted to create an
object, when lead to the current user being set over and over again. It
also meant you had to constantly be aware of what the CurrentUser was in
many different contexts, which was often confusing. Setting creators
explicitly simplifies everything greatly.
Normally we skip doing page counts on index pages when there aren't any
search filters. This is on the assumption that most index pages have
more than 1000 pages (20,000 results), so it's not worth counting them
exactly. This isn't always true, so here we turn on full counts on
certain index pages known to be small.
