feat: reverse shares (#86)

* add first concept

* add reverse share funcionality to frontend

* allow creator to limit share expiration

* moved reverse share in seperate module

* add table to manage reverse shares

* delete complete share if reverse share was deleted

* optimize function names

* add db migration

* enable reverse share email notifications

* fix config variable descriptions

* fix migration for new installations

frontend/src/components/admin/configuration/AdminConfigTable.tsx

@@ -100,7 +100,7 @@ const AdminConfigTable = () => {
                   <Space h="lg" />
                 </>
               ))}
-              {category == "email" && (
+              {category == "smtp" && (
                 <Group position="right">
                   <TestEmailButton />
                 </Group>