Allow copying data from cross-section table, friction table, vegetation table

[leendertvanwolfswinkel]

@ldebek I tested, but something goes wrong. When I use copy, it copies the data to the clipboard as a tab separated table, but pasting only works if there is a comma separated table on the clipboard; if I manually replace tabs by comma's in Notepad, it works.

[ldebek]

@leendertvanwolfswinkel Changes applied.

[leendertvanwolfswinkel]

@ldebek I now get the following error:

AttributeError: 'bool' object has no attribute 'join' 
Traceback (most recent call last):
  File "C:\Users\leendert.vanwolfswin\AppData\Roaming\3Di\QGIS3\profiles\Schema 219/python/plugins\threedi_schematisation_editor\forms\custom_forms.py", line 697, in copy_table_rows
    clipboard_values = "\n".join([separator.join(row_values) for row_values in cross_section_table_values])
  File "C:\Users\leendert.vanwolfswin\AppData\Roaming\3Di\QGIS3\profiles\Schema 219/python/plugins\threedi_schematisation_editor\forms\custom_forms.py", line 697, in 
    clipboard_values = "\n".join([separator.join(row_values) for row_values in cross_section_table_values])
AttributeError: 'bool' object has no attribute 'join'

Private Zenhub Video

[leendertvanwolfswinkel]

@ldebek tested, please merge :)