Help system overhaul

Revisiting the help files (user guide and developer help) is overdue and now luckily a few hours are available.

• New text panel tailored to showing Inishell syntax
• XML syntax highlighting
• New panel to show images
• User guide
  • Describe new features and appearance
  • Clarify workflow
• Dev help
  • Table of content
  • Uniform description of panels with options
  • Copyable code snippets
  • Symbol table
  • Solarized color picker