Enhancement: Logo sizing

We've added theming variables for the max-width and max-height of the OcLogo component and increased the default (max-)height.

https://github.com/owncloud/owncloud-design-system/issues/795
https://github.com/owncloud/web/issues/5128
https://github.com/owncloud/owncloud-design-system/pull/1380
