[BUGFIX] EM: un/install visual feedback

Adds a visual feedback to the un/install button action in EM:
Masks the extension manager during un/install operations
are in progress - after success a page redirect is fired.

Introduces a CSS class that class can be added to any link in EM:
.onClickMaskExtensionManager

Change-Id: If7aa0b15eeab1afb162b103662a10920f4da149f
Fixes: #43856
Releases: 6.0, 6.1
Reviewed-on: https://review.typo3.org/17091
Reviewed-by: Sebastian Michaelsen
Tested-by: Sebastian Michaelsen
Reviewed-by: Tobias Liebig
Reviewed-by: Mattias Nilsson
Tested-by: Mattias Nilsson
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer