Renaming Create Sitemaps page title to be more consistant and removing the
Sitemaps CPT admin page.

Renamed the "Create Sitemaps" page to "Sitemaps" and changed the header on
the page to match the menu name.

Removed the Sitemap custom post type admin page because it had no useful
purpose. See #53 for making this page useful.

Also renamed the sitemap_options() function to
render_sitemap_options_page() so that it was more self descriptive.

In response to comments from @mjangda here:
https://github.com/Mobius5150/msm-sitemap/commit/de3de21d396615001cb8875b2e01735736391207
Adding output escaping to
render_sitemap_options_page() and fixing a couple improperly styled lines.

Adding output escaping to render_sitemap_options_page() as it was missing
output escaping for stats and action buttons on the Sitemaps admin page.

Fixed two badly styled lines in msm-sitemap-builder-cron.php so that they
adhere to the WordPress style guide.