Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/tools/RemovePages.tsx

@@ -0,0 +1,63 @@
+import { useTranslation } from "react-i18next";
+import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
+import { BaseToolProps, ToolComponent } from "@app/types/tool";
+import { useBaseTool } from "@app/hooks/tools/shared/useBaseTool";
+import { useRemovePagesParameters } from "@app/hooks/tools/removePages/useRemovePagesParameters";
+import { useRemovePagesOperation } from "@app/hooks/tools/removePages/useRemovePagesOperation";
+import RemovePagesSettings from "@app/components/tools/removePages/RemovePagesSettings";
+import { useRemovePagesTips } from "@app/components/tooltips/useRemovePagesTips";
+
+const RemovePages = (props: BaseToolProps) => {
+  const { t } = useTranslation();
+  const tooltipContent = useRemovePagesTips();
+
+  const base = useBaseTool(
+    'remove-pages',
+    useRemovePagesParameters,
+    useRemovePagesOperation,
+    props
+  );
+
+
+  const settingsContent = (
+    <RemovePagesSettings
+      parameters={base.params.parameters}
+      onParameterChange={base.params.updateParameter}
+      disabled={base.endpointLoading}
+    />
+  );
+
+  return createToolFlow({
+    files: {
+      selectedFiles: base.selectedFiles,
+      isCollapsed: base.hasResults,
+    },
+    steps: [
+      {
+        title: t("removePages.settings.title", "Settings"),
+        isCollapsed: base.settingsCollapsed,
+        onCollapsedClick: base.settingsCollapsed ? base.handleSettingsReset : undefined,
+        content: settingsContent,
+        tooltip: tooltipContent,
+      },
+    ],
+    executeButton: {
+      text: t("removePages.submit", "Remove Pages"),
+      loadingText: t("loading"),
+      onClick: base.handleExecute,
+      isVisible: !base.hasResults,
+      disabled: !base.params.validateParameters() || !base.hasFiles || !base.endpointEnabled,
+    },
+    review: {
+      isVisible: base.hasResults,
+      operation: base.operation,
+      title: t("removePages.results.title", "Pages Removed"),
+      onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
+    },
+  });
+};
+
+RemovePages.tool = () => useRemovePagesOperation;
+
+export default RemovePages as ToolComponent;