ox-odt.el: Use options instead of hard-coded variables

ox-odt.el: Use options instead of hard-coded variables

* lisp/ox-odt.el (org-odt-content-template-file)
(org-odt-display-outline-level, org-odt-fontify-srcblocks)
(org-odt-format-drawer-function, org-odt-format-headline-function)
(org-odt-format-inlinetask-function, org-odt-inline-formula-rules)
(org-odt-inline-image-rules, org-odt-pixels-per-inch)
(org-odt-styles-file, org-odt-table-styles)
(org-odt-use-date-fields): Replace these hard-coded variables with
options.

(org-odt-do-format-code): Change signature.
(org-odt-fixed-width, org-odt-latex-environment)
(org-odt-format-code): Propagate above change.

(org-odt--image-size): Change signature.
(org-odt-link--inline-image): Propagate above change.

Partial port of commit 3c22bb19e025e350ebcc25c6fc23e2dd59e49693.