New linter rules:
* curly
* block-spacing
* keyword-spacing

Also apply all autofixes introduced by these rules

Our linting config in package.json was:
```
    "extends": [
      "plugin:vue/essential",
      "eslint:recommended"
    ],
```

Now switching to "plugin:vue/recommended" and apply all auto-fixes

this is syntactically more correct.
also the linter does not complain anymore now :)

* facilitate new bootstrap-vue table features to get rid of computed table array
* use template slots of the b-table for better rendering
* button group for edit and delete
* implement delete function

* add filesize npm package
* add prettyNanoseconds mixin function

now displaying files and playlists in a b-table or asking to upload something

also refactored groups to shows, after tank refactoring happened

does not work yet, we always get back a 400 when
logo or image are not null in json format

have to find out how the exact format and encoding has to be to update
a show inlcuding files

When we use the image and logo values in the show object directly,
we get errors, when those values are 0, because they are rendered,
just not visible.

So we use intermediate values now in the this.current object, which
are set everytime the show is switched.