#899 Move "Admin" link to a menu and have an "advanced" mode

[Kim Rutherford]

Replace the "Admin" link with a menu containing:
- the Admin link
- a toggle for "advanced" mode

Advanced mode should be the default for admin and other experienced users but otherwise can be per session.

The only thing I can think of for advanced mode so far is to enable the "Add ..." links for new annotations.

[Kim Rutherford]

I've moved the admin link to a menu (with a gear icon) and added an "advanced" mode toggle. Advanced is on by default for now. It also doesn't get saved so if you turn advanced mode off and reload the page or click a link it goes back to on. I'll fix it so the setting gets stored in the session and defaults to advanced only for admin users.

https://github.com/pombase/canto/commit/9b324ccc50ccd082994276e13b3a4ecd8ad082a6
https://github.com/pombase/canto/commit/d3c793811d877eaf0c59fa11d20b0a5ffbf55d4d

[Kim Rutherford]

The "Advanced" mode setting is now saved so if it's changed it sticks. I've move the login link to the menu too to keep things tidy.

https://github.com/pombase/canto/commit/868ae4276b9098246b3f755f322975820a5dd5ab