Data section refactor

[steven11sjf]

• don't use QTreeWidget as it'll be hard to make editable fields for things like vec3
• separate different "views" into tabs at the top (each actor gets its own tab)
• don't automatically add actors into the view - double-click the actordef link to get that, and double click collision to get that (each in new tabs)
• add "manager" formats for things like brfld, brsa that have multiple data locations
• add dropdowns with multi-selectable subarea setups and collision cameras
• add a way to open arbitrary files (including non-reflection files) in the data editor