Remove dependency on structuremap.

Structuremap was being used to dependency inject a timestamp provider
class for testing.  Removing the dependency on structuremap so that the
project has fewer external dependencies.
Fix accept header in integration tests

Creating the authentication url now requires a proper accept header to
return the html response.
Remove old dependencies
change target framework to .NET4
Merge pull request #1 from dcollied2l/master

Changes to remove structuremap dependency