[BUGFIX] Move EM tabs to function menu

Changes the tabs in extension manager to a function menu.
The views to manage+get extensions are different from a
user perspective.

Change-Id: I2612667cdb2656fa8954b09ada858581318b3c1d
Fixes: #46931
Release: 6.0, 6.1
Reviewed-on: https://review.typo3.org/19563
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Magdalena Leichsenring
Tested-by: Magdalena Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn