Refactor

[andresmgot]

There is a bit of clean-up / refactor that we can do here:

• Converters are no longer needed.
• The Variable/Annotations query editor can be refactored to use a Custom Variable Support rather than the current method isPannelEditor
• The methods to obtain schemas/tables/columns are using sql queries to obtain the data but the AWS API provides functions to do so. In order to follow the same approach for all datasources (and be able to share logic) we should follow that approach.
• After updating the plugin sdk package, we can remove the gtime package from here.