Genericize org-export-html-* variables and other misc changes.

Genericize org-export-html-* variables and other misc changes.

* lisp/org-html.el (org-html-should-inline-p):
Removed. Re-implemented as org-lparse-should-inline-p.
(org-export-html-format-href): Use org-xml-format-href.
(org-export-html-format-desc): Use org-xml-format-desc
(org-export-html-get-tag-class-name): Removed.
(org-export-html-get-todo-kwd-class-name): Removed.
(org-html-get): Added following new per-backend settings
1. INLINE-IMAGES for org-export-html-inline-images
2. INLINE-IMAGE-EXTENSIONS for
   org-export-html-inline-image-extensions
3. PLAIN-TEXT-MAP for
   org-export-html-protect-char-alist
4. TABLE-FIRST-COLUMN-AS-LABELS for
   org-export-html-table-use-header-tags-for-first-column
5. TODO-KWD-CLASS-PREFIX for
   org-export-html-todo-kwd-class-prefix
6. TAG-CLASS-PREFIX for org-export-html-tag-class-prefix

* lisp/org-lparse.el (org-lparse-should-inline-p): New.
(org-lparse-format-org-link): Use INLINE-IMAGE-EXTENSIONS
(org-xml-encode-plain-text): Use PLAIN-TEXT-MAP
(org-lparse-do-format-table-table): Misc change
(org-xml-fix-class-name): New. Extracted from
org-export-html-get-todo-kwd-class-name
(org-lparse-format-todo): Use org-xml-fix-class-name and
TODO-KWD-CLASS-PREFIX.
(org-lparse-format-org-tags): Use org-xml-fix-class-name and
TAG-CLASS-PREFIX.
(org-xml-format-href): Renamed from org-export-html-format-href
(org-xml-format-desc): Renamed form org-export-html-format-desc

* lisp/org-odt.el (org-odt-format-table-cell): Use
TABLE-FIRST-COLUMN-AS-LABELS.
(org-odt-format-inline-image): Use org-xml-format-href.
(org-odt-format-org-link): Use org-lparse-should-inline-p and
org-xml-format-href, org-xml-format-desc.
(org-export-odt-format-image): Use org-xml-format-desc.
(org-odt-get): Provide default values for INLINE-IMAGES,
INLINE-IMAGE-EXTENSIONS, PLAIN-TEXT-MAP,
TABLE-FIRST-COLUMN-AS-LABELS.