Added implementation for SAML Assertion grant

Added implementation for SAML Assertion grant and test cases. Also
updated the sample app to allow user to provide SAML Assertion that can
be consumed by the sample app. -
https://github.com/AzureAD/azure-activedirectory-library-for-objc/issues
/205
Added documentation

Added documentation
Fix for issue #138

Fix for issue#138
https://github.com/AzureAD/azure-activedirectory-library-for-objc/issues
/138
Feature checkin for #213

Feature checkin for
https://github.com/AzureAD/azure-activedirectory-library-for-objc/issues
/213
updated header
Addressed code review comments

Addressed code review comments
Addressed code review comments

Addressed code review comments
Merge pull request #214 from AzureAD/OSXUniversal-Client-Metrics

Feature checkin for #213 (Client Metric reporting)
Merge pull request #210 from AzureAD/OSXUniversal-dev

Pull to Universal Branch - Added implementation for SAML Assertion grant