Add method to retrieve ClickActivity for Campaign

Prior to this it was not possible to get ClickActivity for a campaign
without providing a link id.
Adding .gitignore for VS projects

taken directly from github here:
https://github.com/github/gitignore/blob/master/VisualStudio.gitignore
Test and methods for GetCampaignTrackingClicks

- Added a unit test for the new GetCampaignTrackingClicks method
- Added convenience method to retrieve all clicks for a campaign to
ConstantContact.cs
- Added method to retrieve all clicks to the campaign tracking service
interface
Merge pull request #7 from GoldMineCloud/master

Adding a method to retrieve all clicks from the Email Campaign Service