Fixes in reports (generating a CSV).

Added caching of generated images in mosaico handler.
Various other fixes.

server/lib/synchronized.js

@@ -0,0 +1,26 @@
+'use strict';
+
+// This implements a simple wrapper around an async function that prevents concurrent execution of the function from two asynchronous chains
+// It enforces that the running execution has to complete first before another one is started.
+function synchronized(asyncFn) {
+    let ensurePromise = null;
+
+    return async (...args) => {
+        while (ensurePromise) {
+            try {
+                await ensurePromise;
+            } catch (err) {
+            }
+        }
+
+        ensurePromise = asyncFn(...args);
+
+        try {
+            return await ensurePromise;
+        } finally {
+            ensurePromise = null;
+        }
+    }
+}
+
+module.exports = synchronized;