External User ID Improvements

[OlenaPostindustria]

Motivation

The class PrebidMobile should be used to tune the SDK behavior, such as request timeout.
The class TargetingParams should be used to modify the bid request.

Objectives

1. Deprecate Prebid.externalUserIdArray
2. SDK shouldn't store EIDs in application storage.
3. The structure of ExternalUserId class should be updated according to the standard.