Copyedit GUI building section

[Tom-Willemsen]

• Copyedit the "building the GUI" page to remove outdated information and provide screenshots for clarity
• Copyedit the "Maven and Tycho" page to remove outdated content
  • Link to Maven documentation, in preference to copy-pasting it into our docs, for up-to-date descriptions of how to use Maven
  • Link to our own source code where possible for up-to-date examples of child POMs and application-level POMs
  • Add links to relevant code chat slides/recording.
• Deduplicate troubleshooting notes by linking to existing troubleshooting information, rather than copy-pasting into first-time install guide. This keeps all troubleshooting information logically together.
• Remove "GUI development workflow" as it was an out-of-date duplicate of the standard git workflow and contained misleading steps/screenshots which are no longer appropriate.
• Document how to do redirects, and add redirects for moved/deleted pages

[iangillingham-stfc]

Nice!