Welcome screen, refactor to allow zero documents, and add TS typing to widgets (#702)

* unfinished implementation

* Add frontend for the empty panel screen

* Add an icon for Folder based on NodeFolder

* fixed messages causing peicees of ui not to render on new document

* Standardize nextTick syntax

* WIP generisization of component subscriptions (not compiling yet)

* Fix crash when loading font and there is no active document

* Only advertise tool actions with a document

* Fix failure to create new document

* Initalise the properties panel

* Fix highlight tab, canvas jump, warns and layer tree

* Fix tests

* Possibly fix some things?

* Move WorkingColors layout definition to backend

* Standardize action macro formatting

* Provide typing for widgets in TS/Vue and associated cleanup

* Fix viewport positioning initialization

* Fix menu bar init at startup not document creation

* Fix no viewport bounds bug

* Change !=0 to >0

* Simplify the init system

Closes #656

Co-authored-by: Keavon Chambers <keavon@keavon.com>
Co-authored-by: 0hypercube <0hypercube@gmail.com>

frontend/assets/icon-16px-solid/folder.svg

@@ -0,0 +1,4 @@
+<svg viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
+	<path d="M14,13H2c-0.55,0-1-0.45-1-1V6h5.42l1-1H15v7C15,12.55,14.55,13,14,13z" />
+	<path d="M6,2H2C1.45,2,1,2.45,1,3v2h5l1-1h8c0-0.55-0.45-1-1-1H7L6,2z" />
+</svg>