Deleting model while offline throws an error

[mmacfadden]

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Describe the Bug
When deleting a model offline, we properly delete the model in the offline store, but do not check if we are online or not, and then try to delete the model at the server which throws an exception.

main-app.js:114 TypeError: Cannot read property 'request' of undefined
    at ConvergenceConnection.request (ConvergenceConnection.ts:217)
    at ModelService._removeOnline (ModelService.ts:1216)
    at ModelService.<anonymous> (ModelService.ts:595)
    at Generator.next (<anonymous>)
    at fulfilled (OfflineModelSyncCompletedEvent.ts:25)

We need to check if we are online before trying to call the server.