[notebook] dbproxy_extra_classpath property in hue.ini does not seem respected

It seems like Hue does not respect dbproxy_extra_classpath parameter in notebook section of hue.ini.

It's because in default hue.ini this property located at the end of notebook section, and Hue parsing it as property of following section (i.e. shell):

[notebook]
  ...
  [[interpreters]]
    ...
    [[[shell]]]
       ...
  dbproxy_extra_classpath=/something.jar

Also, there is some problem in Hue 3.12 in librdbms.jdbc.Jdbc class: it fails on initialization when there is no CLASSPATH variable in environment.