Django-ajax-datatable

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* Avoid duplicate column names
* Add a border to "plus" and "minus" icons
* Readme: added an example on how to use extra_data for initial queryset filtering
* Improved layout of global date filters for easier style customization
* Explicitly check field existence when initial order is expressed with fieldnames
* Cleanup full_row_select option
* [fix] Treat DateTimeField properly in filter_queryset_by_date_range()
* App settings for debug tracing renamed

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* Recover missing commits from develp

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* [TODO] check for unwanted side-effects here: ...
* ... Prevent click to move the HTML page to the top
* Improved example project

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* Accept the more generic "pk" column name instead of "id"; "id" still supported for backward compatibility
* In the example project: a new page has been added to play with a model with a custom PK column name

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* classifiers added to setup.py

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* fix Readme