The layout property was used in an enterprise version of the Form editor to have a 12 column layout. In Flowable open source we are not using this property at the moment.
There is an extension for Flowable called Flowable Core Extender Pack that became available recently, which gives advanced Forms engine and Forms design, https://flowable.com/platform/flowable-core/ at bottom of page.
Does this include support for tables and embedded images?