only redirect to dashboard if user has course enrollments, otherwise remain on the course catalog page (aka homepage or root)

update lettuce test to match new expected behavior

add Jason's feedback

only apply new redirect logic for microsites

switch to use a feature flag to determine whether to support redirect behavior
Merge pull request #5220 from edx/cdodge/dont-redirect-to-dashboard-when-having-and-empty-dashboard

only redirect to dashboard if user has course enrollments, otherwise rem...