Payments add modal form

* adds help texts to add payment form
* adds removing button for payments
* refactors user fetching into BaseForm
* adds generic RemoveModalForm which is intended to be used for every modal form which shall remove something
* adds translations
* removes unused html
* prepares payment amount field to be able to process german inputs like '1.000,50' which is not the international default

konova/static/css/konova.css

@@ -194,4 +194,13 @@ input:focus, textarea:focus, select:focus{
 .page-item.active > .page-link{
     background-color: var(--rlp-red);
     border-color: var(--rlp-red);
+}
+
+.label-required{
+    color: var(--rlp-red);
+}
+
+.scroll-300{
+    max-height: 300px;
+    overflow: auto;
 }