Tray icon missing after switch to libappindicator

Recent versions of Dropbox (not yet merged) proclaim loudly that they require libappindicator for tray icon support. OK!

https://help.dropbox.com/installs/dropbox-desktop-app-for-linux

But when I add it to the manifest, the icon is:


This is presumably because the icon name is set to `dropboxstatus-logo` with the theme path set to a sandboxed path:

```
(
{
"AttentionAccessibleDesc": <"">,
"AttentionIconName": <"">,
"Category": <"ApplicationStatus">,
"IconAccessibleDesc": <"">,
"IconName": <"dropboxstatus-logo">,
"IconThemePath": <"/app/extra/.dropbox-dist/dropbox-lnx.x86_64-223.4.4909/images">,
"Id": <"dropbox-client-7">,
"Menu": ,
"Status": <"Active">,
"Title": <"dropbox">,
"XAyatanaLabel": <"">,
"XAyatanaLabelGuide": <"">,
"XAyatanaOrderingIndex":
},
)
```

Not too surprising since libappindicator is not sandbox-aware...