Don't set post_author for scout page to 1.

There's no guarntee that author exists so it's better to leave it out.
create_scout_page should be a private method.
menu_page_url echoes by default. We don't need it to here.
Better sanitization for subscribe widget (bools should be cast as such; all values should be sanitized, etc.)
Remove forced opt-in for sailthru_override_wp_mail

The way it's set up forcefully enables the override on plugin activation with no way to opt-out ahead of time. This should be done opt-in by users.
Better javascript and attribute escaping in follow-up movies
rm unsused metaboxes class
Better escaping for Sailthru Subscribe widget.

Some input values were not being escaped.
rm unused widget.subscribe.ajax template
rm move legacy widget files that are unused
For sailthru_setup_handler, use a whitelist for options.

This way, we don't end up saving arbitrary bits of data we're passed in for added security.
Improve escaping in sailthru_create_dropdown
Improve escaping in sailthru_toggle_feature_callback
Improve escaping in sailthru_html_text_input_callback