Suggest STRICT_ALL_TABLES during setup. Improve dev-mode comments.

Summary: Suggest the MySQL mode STRICT_ALL_TABLES during setup if it is not set. Small improvement to the phabricator.developer-mode comments.

Test Plan: Set the global sql_mode to include or exclude STRICT_ALL_TABLES and check for desired behavior.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4803