enable plugins to choose which screens the Civi button appears on
change filter name as per 175633ea08edc3ed4bbd21e187aec9fb813b0e07
implement thorough post type checking for Civi button
prevent fatal error when `CRM_Core_DAO::executeQuery` called
update docblock for `add_form_button()`
Merge pull request #59 from christianwach/deprecated-function

Civi shortcode button should appear only on those WordPress post types that support the editor