Refactor + minor bugfix in conditional formatting

Use lookup table to translate between listbox positions
and condition modes in the condformat dialog. Use function
to get the number of necessary edit fields instead
of hard-coded if/switch statements.

Fixed minor bug where conditions with no parameter, after
created, would cause one edit field to appear when
opening the dialog, even though it is not used, and would
correctly disappear after selecting the option in the
listbox again.

Change-Id: I7310674162acc33825233866aac3196905dfe8ab
Reviewed-on: https://gerrit.libreoffice.org/13300
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>