The printing function in the PZero terminal is not implemented correctly.

[r-monti14]

With the projections tools, TextTerminal is not working and it freeze the GUI.
In addition, some messages must be review: for istance, when usinig split line-line, the message is "Split line with line. Line to be split has been selected, please select an intersecting line", but to use this tool it is necessary to select the lines to be split and the intersection line before activating the tool.

[r-monti14]

@andrea-bistacchi I saw that you changed some lines in https://github.com/gecos-lab/PZero/blob/class_refactoring_pyside6/pzero/two_d_lines.py moving from self.parent.TextTerminal.appendPlainText() to self.print_terminal().
I test it also in https://github.com/gecos-lab/PZero/blob/class_refactoring_pyside6/pzero/three_d_surfaces.py and seems to be a nice solution. Should I homogenise it in both files?

[r-monti14]

Fixed with 57d72d8
We should check if TextTerminal is used in other files