#199 Open large Chi, CIF, SeText and ToolDef files using text editor.

• Uses default text editor for Chi, CIF, SeText and ToolDef files that are >10 MiB to prevent performance issues.
• Note that:
  • Files keep their custom icons.
  • Files are still by default opened by their own editors.
  • Only larger files are opened by the default text editor.
  • Explicitly opening larger files with their own editor works as expected.
• Documentation updates are from !164 (closed).

Closes #199 (closed)