CampaignService.md

Update to API docs to include:

- new setBannerPaths call
- new "Product" based operation of uploadPlans
- viewing the Products created using getAssignments
- viewing the "uses product policies" flag within a campaign, using getCampaigns
- a couple of spelling or layout fixes
Merge pull request #10 from asharptlm/patch-9

CampaignService.md