org-odt.el: Add support for native numbering of src and example lines

org-odt.el: Add support for native numbering of src and example lines

* contrib/lisp/org-lparse.el (org-lparse-format-org-link):
Push the responsibility of calling
`org-export-get-coderef-format' to the backends.

* contrib/lisp/org-xhtml.el (org-xhtml-format-org-link): Take
up the above responsibility.

* contrib/lisp/org-odt.el (org-odt-format-link): Handle links whose
descriptions are actually line-numbers.
(org-odt-format-source-line-with-line-number-and-label): New.
Generate line numbers and link targets for lines that are part of
source or example blocks.
(org-odt-format-source-code-or-example-plain)
(org-odt-format-source-code-or-example-colored): Use
`org-odt-format-source-line-with-line-number-and-label'.
(org-odt-format-source-code-or-example): Pre-process input lines with
`org-export-number-lines'.  Also handle numbering of src lines.
(org-odt-format-org-link): Rework handling of coderef links.  Generate
ODF-specific markup for line-number based coderef links.
(org-xml-encode-plain-text-lines): Removed.  Not used any more.

contrib/odt/styles/OrgOdtStyles.xml (OrgSrcBlockNumberedLine): New
style for automatic numbering of src and example lines.