Fixes Pitch Page view bug

Fixes #3220 - When a campaign is closed, the pitch page view does not display for the staff-only `node/*/pitch` page.

Cleans up preprocess functions in the meantime, DRY for preprocessing common variables, and moves the `theme_hook_suggestions` declarations into the relevant preprocess functions, to help make `dosomething_campaign_preprocess_node` a little more readable.
This check is no longer needed because of logic in `dosomething_campaign_preprocess_node`, and existing staff only logic in `_dosomething_campaign_pitch_page_access`