Active selections now support multiple non-overlapping shapes

* Renamed Selection data structure. Multiple select begins to work
* Saving and loading of multiple selection shapes implemented
* Renamed Document selection properties to avoid confusion
* Renamed and distributed functions between selection and shape utilities
* Fixes to selection toolbox
* Fixed issue with copying across multiple selections
* Final cleanups

tsconfig.check.json

@@ -1,6 +1,6 @@
 {
     "extends": "./tsconfig.app.json",
-    "includes": [ "src/**/*.ts", "tests/**/*.ts" ],
+    "includes": [ "src/**/*.ts", "src/**/*.vue", "tests/**/*.ts" ],
     "compilerOptions": {
         "skipLibCheck": true
     }