Support for enabling and disabling hide-whitespace
by clicking between page frames.

Disabled header and footer decorators when
hide-whitepsace is enabled, and page size
is trimmed to the contents of each page.

Experimental/suggestive mouse pointers added
but only tested on Windows.

Change-Id: Ia2faeeda9e3e783ffaf5340aa69303a4218892a7
Reviewed-on: https://gerrit.libreoffice.org/18156Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 54a2c8c0)