Provide more helpful errors when i18n generation fails

[turt2live]

Also fix TextForEvent.js so it doesn't break the script. Using a variable here is not recognized, so the object has been moved inline instead.

[bwindels]

fixed the same thing this week but forgot to make a PR out of it :)

[turt2live]

For future people, the exception encountered was:

ERROR: src\TextForEvent.js:236 %(senderName)s added %(addedAddresses)s and removed %(removedAddresses)s as addresses for this room.
TypeError: obj.properties is not iterable
    at getObjectValue (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\scripts\gen-i18n.js:56:28)
    at Object.enter (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\scripts\gen-i18n.js:137:43)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:31:9)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:53:4)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:48:5)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:53:4)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:53:4)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:48:5)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:53:4)
    at visit (C:\Git-updated\_workspaces\riot-web\matrix-react-sdk\node_modules\estree-walker\dist\estree-walker.umd.js:48:5)