Added BugSense

Hello Orta,

Thanks for helping us by writing such a great library of analytics. It contains almost all popular libraries except 'Bugsense' we are frequently using bugsense. So, I decided to add that library into this. I have written basic code of it and tested it. And it is working fine. 

I need your help in one issue. Actually in  BugsenseProvider class App is not able to find path of header. I spent considerable time in fixing it but not able to figured out but as I understand it needs some fix in pod file or podspec. Due to limited knowledge of cocoapod I am not able to fix it. I would be thankful if you can take a look into it.
Once again thanks for your great work. 

I think it's possible that you could receive a nil email address, in which case the provider will crash here, you might want to check for it before appending :+1: