Add admin submenu styles, make "Dashboards" with multi column

[nsotnikov]

The admin dashboards submenu is very long and not optimal styled for bigger screens.
This PR makes it as multi column menu to better fit and reduce scrolling.

Before	After

[bassmaster187]

I like it.
To make sure the new css file will be used and not the old one in the cache I appended a suffix "?v=4"

<link rel="stylesheet" href="static/teslalogger_style.css?v=4">

[nsotnikov]

I like it. To make sure the new css file will be used and not the old one in the cache I appended a suffix "?v=4"

<link rel="stylesheet" href="static/teslalogger_style.css?v=4">

Thanks for hint and commit!