Adding a database url will always add to database list even when invalid

[kinekt4]

Problem
This issue is related to #2178.
A fix (#2180) was made which added an alert box when an error was encountered.
However, the invalid database was added to the database list anyway.
I believe this should not be the case.

Screenshots/Demo
Database list after invalid url was added: https://imgur.com/KxqyLJ1

Athens Version

• https://web.athensresearch.org
• Windows: v2.0.0-beta.34
• Linux: v2.0.0-beta.34

[cortex3]

additionally I think it would improve the user experience if athens could accept full URLs with http://.
This was what I initially tried too and was confused that it didn't work.