Flint: Clean up code around selection API

This MR clean up some code in Flint relative to the plot select API, and bliss<->flint interaction.

• Some clean up here and there
• Refactor GUI side of the selection code
• Rework the API to use events (this removes the 30s max for user edition)
  • For the bliss side API, nothing changes
  • Log message are displayed
  • The selection can be aborted using CTRL-C
• Set the focus to the right tab when user input is requested
• Create integration test for points/shape/ROIs selection
• Plus few clean up
  • Allow to create plot with closeable, selected
  • Clean up messages for stdout/stderr using RPC events