Add features for expandable rows, serverside filters, ability to hide the select all checkbox, and ability to always show the search bar. Also adds various fixes and code cleanup.

• Add onRowsExpand callback #861
• Add isRowExpandable functionality #862
• Add selectableRowsHeader option to show/hide the select all checkbox #882
• Add various options and an example to help make serverside filters more viable #913
• Add searchOpen option to show the search bar at any time https://github.com/gregnb/mui-datatables/pull/893/files
• Fix logic issue with deprecation notices #956
• Fix some issues with downloaded csv data not properly reflected displayed data #964
• Fix issue where serverside sorting would not allow resetting sorted columns to 'none' #971
• Improve accessibility around expandable rows with keyboard functionality like tabbing and enter/space to expand/collapse. Also changes appearance slightly with use of IconButton #970
• Fix various code quality issues #943, #962, #975