Update GUI elements for borehole data in cross section widget

[Huite]

• [x] Add tickBox for "draw as line(s)"; in that case ToolButton presents single, checkable layers (individual tops & bottoms, e.g.)

For borehole data:

• [x] Loop over borehole_data (List[pd.DataFrame]); collect set of df.columns; present in comboBox

• [x] When plotting: only use dataframes that have the selected column

• [x] Add search buffer double spinBox

• [x] Add interpolation resolution double spinBox

• [x] Fix issue if no IPF points are in buffer, which currently errors

• [x] Disable "draw as line(s)" for IPF data (.setEnabled(False))

• [x] Separate plottable data internally:

• for colormesh: self.mesh_x, self.mesh_y, self.mesh_z

• for borehole: self.borehole_x, self.borehole_data, self.borehole_id

• for lines: self.line_x, self.line_y, self. line_id

[Huite]

The design has changed slightly, but functionality has been implemented.