Automatically add HTTP schema to URL when it is missing

**Is your feature request related to a problem? Please describe.**
I copied the URL `192.168.3.8:9227` I used with `curl` into the dejavu connect URL box and wondered why it did not work.
It turned out that dejavu requires the `http://` schema.

**Describe the solution you'd like**
dejavu should automatically prepend the `http://` schema to the URL if it has no schema.

Start at the dejavu connect URL box and trace how its entered URL is validated or passed to the connection request. Done means a URL such as 192.168.3.8:9227 is treated as http://192.168.3.8:9227 while URLs that already include a schema continue to work.

Written by the indexing model from the issue text.