Bunch of changes including mpdf library for creating pdf of invoices. It now attaches a PDF invoice when marked sent. Don't mark invoice_status sent if it partial or paid, removed green text from balance under clients only use red if the client has a balance and some other cleanups were done

composer.json

@@ -0,0 +1,5 @@
+{
+    "require": {
+        "mpdf/mpdf": "^8.0"
+    }
+}