Added custom buttons to admin views, improved the compiler code, with some bug fixes

admin/sql/updates/mysql/2.1.20.sql

@@ -0,0 +1,4 @@
+ALTER TABLE `#__componentbuilder_admin_view` ADD `add_custom_button` INT(1) NOT NULL DEFAULT '0' AFTER `add_css_views`,
+ADD `custom_button` TEXT NOT NULL AFTER `css_views`,
+ADD `php_controller` MEDIUMTEXT NOT NULL AFTER `php_before_publish`,
+ADD `php_model` MEDIUMTEXT NOT NULL AFTER `php_import_setdata`;