add gold_standard attribute to classification

track if the classification was made by a user with an 'expert' role on the project
add project expert classifier method

use project roles scope to determine who an expert classifier is
record gold standard data in classification lifecycle
ensure add gold standard runs in transact!
spec out non-logged in user gold standard behaviour
move to enum field for expert classifier level
add expert level for marking gold standard classification
only update expert_classifier field if gold_standard
use block to setup params on the creatable resource
allow gold_standard attribute to be null
add classification schema validator to lifecycle

use a service object to validate the payload of a classification
reject invalid classification payloads
run schema validation via classification model validations

The model should know how to validate itself and if not valid should never reach the later lifecycle events in the background workers.
ensure consistent db schema after rebase
consolidate migrations
pretty array string formatting
Merge pull request #245 from camallen/gold_standard_in_classification

add gold standard flag to classification