Switch column type after import

[thinkh]

At the moment the user chooses the column type in the import dialog. When we import data directly we have to allow the user to switch column types after import (e.g., if categorical is a string, etc.).
This should be done on click on the visual marker (see Caleydo/lineup#25).

[thinkh]

• Add a custom button with callback and item position to the more menu as hook in LineupJS
  • Click on the guessed indicator ("?") opens a menu with option to approve column type
  • Add another hook for this menu
• Callback should open select column type and configuration from phovea_importer dialog
• If column type has changed: remove current column at position and add new column type at the same position (code in lineup)

[mstreit]

Oh yes, this would be a very cool feature!