Table/Dataframe viewer improvements

[tlambert03]

@kevinyamauchi's wish list from napari/napari#3512 (comment)

high priority"

• Inputs: pandas DataFrame and a dict of numpy arrays
• Outputs: pandas DataFrame and a dict of numpy arrays
• Events:
  • value changed
  • cell selected
  • row selected
  • column selected, others?
• Style: I don't have super concrete thoughts here, but
  • I think it should be easy for the user and devs to change the styling (e.g., fonts and font sizes) since the size of the tables and table values are going to vary widely.
  • For numeric values, I think it would be useful to specify the precision to avoid super wide float columns (perhaps similar to how it is done in formatted strings). (https://github.com/napari/magicgui/pull/301?)

"nice to have" (in rough order of my priority)

• allow the columns to have types (https://github.com/napari/magicgui/issues/216). bonus points for being able to attach a validator function.
• ability to "split" (e.g., keep the header row in view while the rest of the table scrolls)
• allow colormaps to be attached to columns to color cells by value
• lazy loading
• a "search bar" the user can use to query the table