fix type of EventData.applicationProperties

[SreeramGarlapati]

Addresses (#49)
This PR fixes an AMQP spec violation for the AmqpMessage Properties, which is also a breaking change.

3.2.5 Application Properties:

The keys of this map are restricted to be of type string (which excludes the possibility of a null key) and the values are restricted to be of simple types only, that is, excluding map, list, and array types.

[msftclas]

Hi @SreeramGarlapati, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

It looks like you're a Microsoft contributor (Sreeram Kumar Garlapati). If you're full-time, we DON'T require a Contribution License Agreement. If you are a vendor, please DO sign the electronic Contribution License Agreement. It will take 2 minutes and there's no faxing! https://cla.microsoft.com.

TTYL, MSBOT;