I added a new submenu under MS compatible Forms menu called Legacy Forms.
Under this submenu user can insert the three legacy form fields. These
fields were already supported by DOC / DOCX filters, but were missing from
the UI.
When inserting text form field we insert 5 enspace to make the
field visible, otherwise we use the same insertion methods what is
called by DOC import.

Change-Id: I1fb8c03d969b4c547ca92e783ac5e216767685d5
Reviewed-on: https://gerrit.libreoffice.org/67907
Tested-by: Jenkins
Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>