v1.0.0-beta.8

Fixes a number of issues that came up in beta 7:

• Made the text column filter work as expected when a search term is applied in the filter control (#135, #144, #145)
• Added support for columns containing multiple types of data (previously this locked up the widget when sorting) #133
• Made the add row button works as expected when the grid is not sorted by the index #132
• Fixed the issue where resizing a column had a side effect of clicking the column header, which resulted in a sort being triggered #134
• Convert objects to strings before attempting to display them to fix #57
• Added new get_selected_df method to provide a more convenient alternative to get_selected_rows which reflects any filtering/sorting changes #137
• Bumped the required pandas version to address #139