Bad dropapp.json causes unclear error message

[teleclimber]

Bad JSON file, like:

{
    "name": "Tuto Test App"
    "version": "0.1.0"
}

Results in this in ds-dev

• "Error processing app" (OK)
• "internal error while reading file metadata, see log" (OK)
• No message in log apart from "Reprocessing app version metadata" (not nice).

Error should be more clear that it's a json parse error.

Note all this is moot if we ditch dropapp.json