[BUGFIX] Add reserved area for loading indicator within modules

The DocHeader has now a reserved area for the nprogress loading
indicator for use within modules. The area has a fixed position to
ensure visibility in every case.

The code of the Recycler and Extension manager have been adjusted
to use that element for the progress bar.

Resolves: #71509
Releases: master, 7.6
Change-Id: I07cacf61a1634357d4da0fe292ea22ba34a6100e
Reviewed-on: https://review.typo3.org/45199


Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>