fix script revert activating recommendation level

Reverting any single of the scripts from standard recommendation pool
shows "Standard" selection as selected which is wrong. This commit fixes
it, refactors selection handling in a separate class and it also adds
missing tests. It removes UserSelection.totalSelected propertty in favor of using
UserSelection.selectedScripts.length to provide unified way of accessing
the information.

tests/unit/stubs/UserSelectionStub.ts

@@ -0,0 +1,49 @@
+import { IUserSelection } from '@/application/Context/State/Selection/IUserSelection';
+import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
+import { IScript } from '@/domain/IScript';
+import { IEventSource } from '@/infrastructure/Events/IEventSource';
+import { EventSource } from '@/infrastructure/Events/EventSource';
+
+export class UserSelectionStub implements IUserSelection {
+    public readonly changed: IEventSource<readonly SelectedScript[]> = new EventSource<readonly SelectedScript[]>();
+    public selectedScripts: readonly SelectedScript[] = [];
+    constructor(private readonly allScripts: readonly IScript[]) {
+
+    }
+    public withSelectedScripts(selectedScripts: readonly SelectedScript[]) {
+        this.selectedScripts = selectedScripts;
+    }
+    public areAllSelected(): boolean {
+        throw new Error('Method not implemented.');
+    }
+    public isAnySelected(): boolean {
+        throw new Error('Method not implemented.');
+    }
+    public removeAllInCategory(): void {
+        throw new Error('Method not implemented.');
+    }
+    public addOrUpdateAllInCategory(): void {
+        throw new Error('Method not implemented.');
+    }
+    public addSelectedScript(): void {
+        throw new Error('Method not implemented.');
+    }
+    public addOrUpdateSelectedScript(): void {
+        throw new Error('Method not implemented.');
+    }
+    public removeSelectedScript(): void {
+        throw new Error('Method not implemented.');
+    }
+    public selectOnly(scripts: ReadonlyArray<IScript>): void {
+        this.selectedScripts = scripts.map((s) => new SelectedScript(s, false));
+    }
+    public isSelected(): boolean {
+        throw new Error('Method not implemented.');
+    }
+    public selectAll(): void {
+        this.selectOnly(this.allScripts);
+    }
+    public deselectAll(): void {
+        this.selectedScripts = [];
+    }
+}