[core] Configuration of connectors via the interface

• List of classes of connectors via ini
• Instances of connector via interface
• Clean Configuration page (horizontal, search etc)
• Only list configs of installed connector on Config page + Spotlight search (Sections/Fixed width or .../All section)

Current list of connectors: https://github.com/cloudera/hue/blob/master/desktop/core/src/desktop/lib/connectors/types.py

To enable:

[desktop]
enable_connectors=true 

Optional: to have some initial connectors loaded at startup:

[[connectors]]

[[[mysql-1]]]
nice_name=MySql
dialect=mysql
settings='[{"name": "url", "value": "mysql://hue:hue@gethue.com:3306/hue"}]'

[[[hive-2]]] 
nice_name=Hive 
dialect=hive 
settings='[{"name": "server_host", "value": "gethue.com"}, {"name": "server_port", "value": 10000}]'