Adds functionality to increment traits if set

[ladanazita]

Supports Amplitude's add functionality. Will add a new setting traitsToIncrement to UI, which will accept an array of traits (of type NSString) to check in identify.traits. If the trait is present, it will increment the trait given the value passed in.

This will increment a user property by some numerical value. If the user property does not have a value set yet, it will be initialized to 0 before being incremented.

[f2prateek]

The long form and short form usage seems to be inconsistent, we're using both for the changes in this PR - can we stick to one (preferably short form)?

[f2prateek]

This seems inefficient. The runtime is O(n*m) where n = size of payload.traits and m = size of settings.traitsToIncrement.

You should remove the case insensitivity and we can cut the runtime to O(n).

[f2prateek]

This could be faster and run in o(n). Looks good otherwise.

[ladanazita]

Updates so that for each trait passed in identify and appears in traitsToIncrement, use add otherwise, use set. if traitsToIncrement is not configured, fallback to setUserTraits, which wraps the set functionality, allowing you to set an NSDictionary of user traits at once

[brennan]

Wouldn't we have to remove incremented traits from the traits object? From Amplitude's docs: "Note: If a user property is used in multiple operations on the same Identify object, then only the first operation will be saved and the rest will be ignored. " setUserProperties isn't called on an Identify object, so I'd expect that traits set via this method would override any traits already incremented on the Identify object.

[brennan]

Clarification from Amplitude's docs: "You may use setUserProperties shorthand to set multiple user properties at once. This method is simply a wrapper around Identify.set and identify." That said, calling setUserProperties creates its own instance of the Identify class in Android.

[ladanazita]

Hmm I don't call setUserProperties if settings has values in traitsToIncrement . Instead it moves into the incrementTrait block and uses set. Yup, setUserProperties is just a wrapper around the logic of using set on AMPIdentify.