[EventCalendar] Bug in class definition of wrappers

[Max Ackermann]

Hi all,

There is a bug in the admin.php where the class definitions are not
correctly defined, which makes the box undraggable:

Search for these:
    <div class="dbx-box-wrapper">
    <div class="dbx-handle-wrapper">
    <div class="dbx-content-wrapper">

And replace them with:
    <div class="dbx-b-ox-wrapper">
    <div class="dbx-h-andle-wrapper">
    <div class="dbx-c-ontent-wrapper">

Best, Max