Azure Mobile Service Error

The app was breaking when an incorrect Mobile Service Address or
Application Key was given, even if enableAzureMobileService was set to
false. I just added an if-statement that checks to see if Azure is
enabled before trying to create the client. I also added in an async
message if Azure is enabled and the key/address is still incorrect.
Fixed RSS Service

If a bad RSS feed is added to the RssAddressCollection, any RSS feeds
following it would occasionally not be loaded. I moved the try-catch
statement in the RssService GetItems method to wrap just the part where
the feed is parsed. Before, if it broke on a bad feed, it would return
the results before parsing through the rest of the addresses.

I also fixed the Tumblr example, which is what caused me to find the bug
in the first place. (The blog I was pulling from decided to change their
address.)
Merge pull request #8 from winappkits/master

Pull Request
Merge pull request #18 from acrow59/master

Fix minor Bugs in AMS & RSS Service