Initial migration to typescript (#845)

This migrates some utilities classes from javascript to typescript.
Nothing special about the migration, mainly added types and made sure
the code adheres to the strict mode.

I have picked some small files so git doesn't think they are the same
since they are "very different".
I hope that in later PRs, when migrating lager files this won't be an
issues.

src/libs/document-uid.ts

@@ -0,0 +1,9 @@
+/**
+ * A unique id for the current document.
+ */
+let REF = 0;
+
+export default function generateUniqueId(prefix="") {
+  REF++;
+  return prefix+REF;
+}