UpdateManager configuration

- Implemented UpdateManagerConfiguration class to store the
configuration data specific to UpdateManager
- This class can be serialized and de-serialized into/from xml file.
- UpdateManager initializes the configuration from
UpdateManagerConfig.xml file if present in Dynamo installation,
otherwise by default it will point to production servers for
UpdateFileLocations and Signature file location.
- In Debug build it creates UpdateManagerConfig.xml file if not present
and saves the default configuration data. The same file can be used to
redirect the update location to the dev S3-bucket from a release build.

Merges:

- [ ] Revit2015

PTAL:
- [ ] @ikeough 
- [ ] @lukechurch  
Slightly ambiguous name, this is the name of the place where the installer is to be downloaded from?

If so - DownloadSourceURI?