Add a down arrow next to user name to show dropdown options and ensure it works on all pages

[mariobehling]

Currently it is not clear that there is a dropdown menu for the user. Therefore add a triangle next to the username.

At the moment the dropdown does not work during creating orders. Ensure it works also then.

1. The first part of the issue is to add it on the "public" ticket pages.
2. The second part is to also add the arrow into the organiser views.
3. Expected is also that one click open the menu, the second click closes the menu (just like on eventyay.com).

[mariobehling]

The first PR solves the first part of the issue. The second part is to also add the arrow into the organiser views. Expected is also that one click open the menu, the second click closes the menu (just like on eventyay.com).

[mariobehling]

Ok, I already opened an issue for the admin part here #371

Therefore just ensure that the menu open on one click and closed on another click, please.