Displaying the number of standardized pages in the Word count window

The number of standardized pages (unit defined in the options)
for the entire document and the selected area is displayed
(if enabled in options) in the Word count window.
The number of pages of size P for an area containing N characters equals P/N.
This value is a float with one decimal place precision.
The default size of the standardized page is 1800 characters
(including whitespace characters).

The configuration can be altered in Options->Writer->General.

Conflicts:
	sw/source/ui/config/optload.cxx

Change-Id: If13e87c73cb7706ff6618fa0352ba29c7c670aec
Reviewed-on: https://gerrit.libreoffice.org/7642
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>