Mass Edit

It'd be nice to be able to provide a command to mass edit data within the dataframe. In the pokemon dataframe, lets say I want to change any pokemon with the "Char" in its name to have a Generation of 0 for some reason. I see two possible ways to do this, with option 2 being my preference as it gives the user great power.

1) Filter what you want to edit (provide 'Name'.str.contains('Char') to the filter field) then provide a value (0) in another field to push to the column of interest (Generation) for all rows displayed from the filter option applied.

2) Allow user to provide full command and update display. i.e. provide something like
`pokemon.loc[pokemon['Name'].str.contains('Char'), 'Generation'] = 0`
somewhere in the gui and then execute. If this option is provided, it should be similar to filter imo where the command is stored and can be re-run or modified before re-running. This would pair nicely with implementation of the enhancement I documented in issue #232 where a user can export commands that they may use frequently so they can import common commands into other dataframes.