Implement Select All/Deselect All layers (#242)

* Implement select all layers shortcut

* Adjust menu entry for Select All Layers

* Avoid selecting the root of the document when selecting all layers

* Implement deselect all layers

* Fix formatting

* Add extensions.json so VS Code recommends useful extensions

* Add rust-analyzer as the default Rust formatter

.vscode/extensions.json

@@ -0,0 +1,3 @@
+{
+    "recommendations": ["matklad.rust-analyzer", "dbaeumer.vscode-eslint", "octref.vetur", "formulahendry.auto-close-tag"]
+}

.vscode/settings.json

@@ -1,7 +1,8 @@
 {
 	"[rust]": {
 		"editor.formatOnSave": true,
-		"editor.formatOnPaste": true
+		"editor.formatOnPaste": true,
+		"editor.defaultFormatter": "matklad.rust-analyzer",
 	},
 	"[typescript, javascript, json, vue]": {
 		"editor.codeActionsOnSave": {