[TASK] Add save only button to Scheduler task

Scheduler tasks currently miss a save only button. Since Firefox and
Opera don't send the value of an <input type="submit">, the save and
save & close buttons are wrapped in a <button type="submit"> to ensure
saving and saving & closing is cross-browser compatible.

Change-Id: Ia5e32efc2e5e2af2943374c9a570a3a94b0511b4
Fixes: #44152
Releases: 6.1, 6.0, 4.7
Reviewed-on: https://review.typo3.org/17681
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn