JRuby support

[katafrakt]

This is a tracking issue for initiative of making Hanami CLI compatible with JRuby. This is probably the largest step in making the whole framework compatible.

To my knowledge, this is what needs to be done:

• Build assets without using fork (Use threads instead of forking to compile slices assets #404)
• Correctly recognize and handle JDBC drivers
• SQlite3 JDBC compatibility
• MySQL JDBC compatibility
• PostgreSQL JDBC compatibility