For multi-column sections in Writer, HTMLMODE_FRM_COLUMNS controlled
whether column settings for the section were exported to html or not.
This was disabled for Internet Explorer and enabled for other browsers.

The export was implemented using non-standard MULTICOL html element
and did not actually work in any modern browser (apparently only
some versions of Netscape have ever supported this). This patch

 - exports the column count also using "column-count" CSS attribute
   which is supported by latest versions of Opera and IE. Firefox and
   Webkit based browsers would currently require -moz-column-count and
   -webkit-column-count but I have not added these since the browsers
   will likely stop requiring the prefix in the future anyway.
 - removes HTMLMODE_FRM_COLUMNS conditional so that this export will
   happen with all html compatibility options, including IE.

Remaining issue: Using the MULTICOL element (as opposed to DIV element)
confuses at least Opera so that it ignores all style attributes applied
on the element. But corresponding html import code in LibreOffice still
relies on MULTICOL. I will work on a separate patch to add support for
column-count CSS attribute to the import code and switch export to use
DIV instead.

Change-Id: I82a065fdda0e074fbfcd0007e6ff6e46185be3f5
Reviewed-on: https://gerrit.libreoffice.org/2950Reviewed-by: Petr Mladek <pmladek@suse.cz>
Tested-by: Petr Mladek <pmladek@suse.cz>