Extract defaultProps from a config file

[Vincent]

As discussed with @loicteixeira it would be easier and more future proof to extract duplicated defaultProps to a global config file:

wagtailmodelchoosers/wagtailmodelchoosers/client/components/BaseChooser.js

Lines 14 to 19 in 11ea65f

 display: 'title', 
 filters: [], 
 translations: {}, 
 pk_name: 'uuid', 
 page_size: 10, 
 page_size_param: 'page_size', 

wagtailmodelchoosers/wagtailmodelchoosers/client/components/ModelPicker.js

Lines 22 to 25 in fe0b76e

 filters: [], 
 page_size: 10, 
 page_size_param: 'page_size', 
 translations: {}, 

[Loic Teixeira]

FWIW, the reason why we can't just set the props as optional with default in BaseChooser and mark the props as required in ModelPicker is because ModelPicker is used directly (not through BaseChooser) from DraftJS. Therefore we need to accommodate that some options might not be supplied.