Improve layout of random number generator dialog

New widgets arrangement in Calc - Edit - Fill - Random Numbers dialog.
I placed  the distribution parameters closer to the distribution combo box.
Custom Seed and Decimal Places are now global options for the generators.
Help page for the new layout will follow.

Change-Id: I0d3f4c09b2c172271b675078abca6013c35a1da2
Reviewed-on: https://gerrit.libreoffice.org/11206
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>