v9.3.0

• Convert all intree components to new Symfony Forms-based datamanager
• update bundled JS dependencies (elFinder, CodeMirror)
• implement support for subtasks in project management & sales/invoicing
• basic iCal create & edit support
• more testcases and improved coverage
• unbundling of optional components (DM2, tmp service, positioning)
• Converted content cache & attachment serving to Symfony HTTP Foundation
• many cleanups, API streamlining, small fixes and simplifications