Removed casting of an NSArray to NSMutableArray

- Goes with 3ea5606 to fix #60
- Sauce: https://lists.apple.com/archives/java-dev/2005/Jan/msg00543.html
Optional name or id for trackScreenView
Sets resolution in terms of actual pixels
Removed auto increment from event table.

Ref: http://stackoverflow.com/questions/10727541/running-out-of-unique-ids-in-sqlite-database
Fixed the ecommTransactionItem in ecommTransaction
Better set timestamps with setTimestamp:toPayload: