Introduce some new hooks.

Add some hooks at some key points in the liveblog flow which can be useful for manipulating the behaviour or things like stats tracking. Some hooks include:

* liveblog_insert_entry
* liveblog_update_entry
* liveblog_delete_entry
* liveblog_preview_entry
* liveblog_enable_post
* liveblog_disable_post
* etc.

liveblog.php

@@ -233,6 +233,8 @@ public static function ajax_entries_between() {
 		// Get liveblog entries within the start and end boundaries
 		$entries = self::$entry_query->get_between_timestamps( $start_timestamp, $end_timestamp );
 		if ( empty( $entries ) ) {
+			do_action( 'liveblog_entry_request_empty' );
+
 			self::json_return( array(
 				'entries'           => array(),
 				'latest_timestamp'  => null
@@ -254,6 +256,8 @@ public static function ajax_entries_between() {
 			'latest_timestamp'  => $latest_timestamp,
 		);
 
+		do_action( 'liveblog_entry_request', $result_for_json );
+
 		self::json_return( $result_for_json );
 	}
 
@@ -382,20 +386,23 @@ public static function ajax_insert_entry() {
 		// Are we replacing an existing comment?
 		if ( !empty( $replaces_comment_id ) ) {
 
-			//
 			add_comment_meta( $new_comment_id, WPCOM_Liveblog_Entry::replaces_meta_key, $replaces_comment_id );
 
 			// Update an existing comment
 			if ( !empty( $entry_content ) ) {
+				do_action( 'liveblog_update_entry', $replaces_comment_id, $new_comment_id, $post_id );
 				wp_update_comment( array(
 					'comment_ID'      => $replaces_comment_id,
 					'comment_content' => wp_filter_post_kses( $entry_content ),
 				) );
 
 			// Delete this comment
 			} else {
+				do_action( 'liveblog_delete_entry', $replaces_comment_id, $post_id );
 				wp_delete_comment( $replaces_comment_id );
 			}
+		} else {
+			do_action( 'liveblog_insert_entry', $new_comment_id, $post_id );
 		}
 
 		$entry = WPCOM_Liveblog_Entry::from_comment( get_comment( $new_comment_id ) );
@@ -412,9 +419,13 @@ public static function ajax_insert_entry() {
 	function ajax_preview_entry() {
 		self::ajax_current_user_can_edit_liveblog();
 		self::ajax_check_nonce();
+
 		$entry_content = isset( $_REQUEST['entry_content'] ) ? $_REQUEST['entry_content'] : '';
 		$entry_content = wp_filter_post_kses( $entry_content );
 		$entry_content = WPCOM_Liveblog_Entry::render_content( $entry_content );
+
+		do_action( 'liveblog_preview_entry', $entry_content );
+
 		self::json_return( array( 'html' => $entry_content ) );
 	}
 
@@ -648,13 +659,13 @@ public function save_meta_box( $post_id ) {
 		if ( empty( $_POST[self::nonce_key] ) || ! wp_verify_nonce( $_POST[self::nonce_key], self::nonce_key ) )
 			return;
 
-		// Update liveblog beta
-		if ( ! empty( $_POST['is-liveblog'] ) )
+		if ( ! empty( $_POST['is-liveblog'] ) ) {
 			update_post_meta( $post_id, self::key, 1 );
-
-		// Delete liveblog meta
-		else
+			do_action( 'liveblog_enable_post', $post_id );
+		} else {
 			delete_post_meta( $post_id, self::key );
+			do_action( 'liveblog_disable_post', $post_id );
+		}
 	}
 
 	/** Error Methods *********************************************************/