#589342: Introduce page_manager_get_current_page() to get information about the current page manager page.

Also forgot to merge a todo in last commit.

First steps toward updating CTools to d7. This contains some stuff found by coder module, plus css.inc should be fully ported. No testing performed though, so theres probably bugs. Need to write some tests or something.

- php potx-cli.php --mode=multiple
- msgcat views_content-plugins-content_types.pot views_content-plugins-views.pot views_content.pot --use-first --no-wrap -o views_content.combined.pot
- msgcat page_manager-plugins-tasks.pot page_manager-theme.pot page_manager.pot --use-first --no-wrap -o page_manager.combined.pot
- msgcat ctools.pot includes.pot plugins-access.pot plugins-arguments.pot plugins-content_types-block.pot plugins-content_types-custom.pot plugins-content_types-form.pot plugins-content_types-node.pot plugins-content_types-node_context.pot plugins-content_types-node_form.pot plugins-content_types-term_context.pot plugins-content_types-user_context.pot plugins-content_types-vocabulary_context.pot plugins-contexts.pot plugins-relationships.pot --use-first --no-wrap -o ctools.combined.pot

Make sure that tasks that will not override existing overrides refuse to enable and provide an error message saying why.

#528022 by tha_sun: Change wording of "Add variant" to "Create variant" to avoid confusion with the "Add variant" tab.