geometry: Copy/Paste with system clipboard.

src/Model/Except.py

@@ -116,3 +116,44 @@ class FileFormatError(ExeceptionWithMessageBox):
             _translate("Exception", "format because of") +
             f" '{self.reason}'"
         )
+
+
+class ClipboardFormatError(ExeceptionWithMessageBox):
+    def __init__(self, mime=None, header=None, data=None):
+        super(ClipboardFormatError, self).__init__(
+            title = _translate("Exception", "Clipboard format error")
+        )
+
+        self.mime = mime
+        self.header = header
+        self.data = data
+
+        if self.mime is not None:
+            self.msg = f"Impossible to decode data to mime code '{self.mime}'"
+        else:
+            if len(self.header) == 0:
+                msg = _translate("Exception", "without header")
+            else:
+                msg = (
+                    _translate("Exception", "with header") +
+                    f": {self.header}"
+                )
+
+                self.msg = (
+                    _translate("Exception", "Invalid clipboard data format:") +
+                    f" '{self.data}' {msg}"
+                )
+
+        self.alert()
+
+    def __str__(self):
+        return self.msg
+
+    def header(self):
+        return _translate("Exception", "Clipboard format error")
+
+    def short_message(self):
+        return _translate("Exception", "Clipboard format unknown")
+
+    def message(self):
+        return self.msg