* Added new DocumentResponse variant
* Update Operation::DeleteSelectedManipulatorPoints to update Layer Tree by delegating deletion to Operation::DeleteLayer. Also emits Operation::DeletedSelectedManipulatorPoints to let editor clear Properties panel
* Update process_message() to deal with new DocumentResponse::DeletedSelectedManipulatorPoints match case. When this DocumentResponse is emitted, it clears the Properties panel.
* Added Display trait implementation for DocumentResponse::DeletedSelectedManipulatorPoints. Updated imports in document_message_handler.rs to get the correct types for messages emitted from DocumentResponse::DeletedSelectedManipulatorPoints match case in process_message().
* Removed useless import. Capitalized comments for style consistency.
* Updated messages emitted to clear Properties panel by emitting LayoutMessage::SendLayout's instead, which update the backend widget state
* Revert inclusion of unused imports
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Co-authored-by: Keavon Chambers <keavon@keavon.com>
* Fixes issue of hints not closing when all documents are closed
* Fix whitespace and rewrite comment
* Close tool hints when you close all documents by doing File->Close All
