Now extension installation via the Extension Manager dialog can be
dynamically enabled/disabled from the expert configurations.

This also affects the installation by double-clicking the extension
file in the file manager, but doesn't affect the unopkg commands.

Change-Id: I70c2c83c2458115b366c7fdcc06f72e11df4726b
Reviewed-on: https://gerrit.libreoffice.org/36688Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Muhammet Kara <muhammet.kara@pardus.org.tr>