Updates to the measurement exporter and its UI, including a new checkbox to export project metadata.

This addresses #2057 (albeit without the flexibility to choose specific metadata values - it's all or nothing). @zindy

Combined with other PRs, it also

• Supports gzipped output (add .gz to the end of the path)
• Attempts to handle escaping whenever the separator (or a double quote) appears within a cell
  • For a tab-delimited file, a tab is replaced by \t
  • For another file (comma or semicolon delimited), if a cell contains the delimiter or a double-quote it will be surrounded by double quotes, and any existing ones will be escaped as ""
• Makes many selections persistent preferences, so they are not immediately reset
  • The output file path is a special case: this will reset when a project changes if its value is currently within the project directory.
    • The aim is to avoid resetting the path if a user is exporting to any arbitrary directory, but also not to default to a previous directory for a different project than the one currently open.