org-odt.el: Typeset display equations using tables

org-odt.el: Typeset display equations using tables

* contrib/odt/styles/OrgOdtContentTemplate.xml: Add bottom
margin to "OrgTable".  Modify border properties of
"OrgTblCell*"s.  Add "OrgEquation" table styles for
typesetting of display equations.

* contrib/odt/styles/OrgOdtStyles.xml: Added various "graphic"
styles for formatting of inline and display equations.
Modified names of some "graphic" styles for images for reasons
of consistency.

* contrib/lisp/org-odt.el (org-export-odt-do-format-image):
Removed.  This is now folded in to
`org-export-odt-format-image'.  A part of this is extracted in
to `org-odt-format-entity'.
(org-odt-entity-frame-styles): New variable.
(org-odt-format-entity): New function.  See previous entries.
(org-export-odt-format-image): Modified.  See previous
entries.
(org-export-odt-do-format-numbered-formula)
(org-export-odt-do-format-formula): Removed.  These functions
are now folded within `org-export-odt-format-formula'.
(org-export-odt-format-formula): Modified as noted above.
Also use `org-odt-format-entity'.
(org-odt-format-frame, org-odt-format-textbox): Modified
signature to facilitate elegant introduction of
`org-odt-format-entity'.
(org-odt-format-inlinetask): Honor change in signature.
(org-odt-label-def-ref-spec): Added an entry for "Equation".

Only MathML equations are typeset using tables.  Dvipng equations are still
typeset as regular images.