Add bundlechange App that takes care of customers upgrades and
downgrades. Changes: limitmonitor.common module: * Add billing_period to parse_subscription * Add get_variation, order_paid and cancel_subscription limitmonitor.task_resources.subscription: * Process pending_regs in reverse order * Add upgrade_user_subscription and process_bundle_changes limitmonitor.views: * Add can_upgrade control middleware.settings: * Add BundleChange app * Add new config variable for BundleChange purist: * Rename DeleteAcccountForm for reuse * Add display names to AccountType * Move spinner animation into a single template in purist module for reuse Signed-off-by: Birin Sanchez <birin.sanchez@puri.sm>