* add unit tests
* add test structure
* add unit tests for Registry
* add LoaderRegistry unit test
* add unit test for makeSingleton
* add type check
* add plugin data structures
* simplify API
* add preset tests
* update test message
* fix lint
* update makeSingleton
* update Plugin, Preset and unit test
* revise Registry code
* update unit test, add remove function
* update test
* update unit test
* update plugin unit test
* add .keys(), .entries() and .entriesAsPromise()
* update test description
* reactify world map
* add createAdaptor
* fix typo
* add schema
* move directory
* remove unnecessary lines
* make setRef a function
* convert keys to camelcase
* add unit test
* update formatting
* add check for displayName
* pass width and height as separate inputs
* [WiP] [explore] proper filtering of NULLs and ''
TODO: handling of Druid equivalents
* Unit tests
* Some refactoring
* [druid] fix 'Unorderable types' when col has nuls
Error "unorderable types: str() < int()" occurs when grouping by a
numerical Druid colummn that contains null values.
* druid/pydruid returns strings in the datafram with NAs for nulls
* Superset has custom logic around get_fillna_for_col that fills in the
NULLs based on declared column type (FLOAT here), so now we have a mixed
bag of type in the series
* pandas chokes on pivot_table or groupby operations as it cannot sorts
mixed types
The approach here is to stringify and fillna('<NULL>') to get a
consistent series.
* typo
* Fix druid_func tests
* Addressing more comments
* last touches
