Add drop down for replace, remove Column_Selector

[jdunkerley]

Pull Request Description

• Add dropdowns for replace functions.
• Retire Column_Selector type.
• Add select_blank_columns and remove_blank_columns functions to table types.
• Allow Regex to be used to pick columns.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.

[radeusgd]

I feel like I'd sometimes want to distinguish between a "" and Nothing - depending on context these may have some different meaning - e.g. in database NULL vs empty string are different entries and they can mean different things.

Do you think we should add treat_empty_string_as_blank like treat_nan_as_blank?

I'm not strongly attached to it since this can be emulated relatively easily using more primitive operations. So whatever you think will be better.

[jdunkerley]

This was be design when we agreed the previous API design for removing blank values.

I appreciate there is a difference but the single value case can easily be done using the filter API.

[radeusgd]

Looks great and the usages look much cleaner with the new approach! ❤️