improve dataframe UI #2836. Data bars, heatmap, changing precision

[mnavasiolava]

this PR contains the following changes

1. keyboard bindings
   • digit 1-9: set precision, number of digits shown.
   • b to show bar chart in bkg of all cells in current column.
   • h to show heatmap in bkg of current column.
2. column menu was changed:
   • 'Format' -> 'double 2 decimals', 'double 4 decimals' menu items were deleted, instead of them new item 'double with precision' was added
   • 'Style' -> 'Data Bars' and 'Heatmap' menu item were added
3. rows selection was fixed (difference between the index and regular columns)
4. rows highlighting was fixed
5. fix for opening multilevel dropdown menu

[scottdraves]

👍