Fixed bug with cut, copy and paste commands.

Pressing the command key was forcing the editor to deselect text and move the cursor to the end of the line.

Refs #1839
Fixed bug with backspace.

Backspace was not properly deleting selected text if the selection went up to the start of the editable line.

Refs #1839
Adding code to terminate pasting if an error is encountered.

Refs #1839
Merge remote branch 'origin/bugfix/1839_fix_cut_copy_commands_in_script_interpreter'