adds opt in setting for WPAnalytics
Merge branch 'develop' into issue/1829-mixpanel_opt_out
NUX: check username, prmopt for self-hosted if reserved.
removes duplicate mention of "self-hosted"
Merge pull request #1833 from wordpress-mobile/issues/1805-selfhosted-signup

NUX: check username, prmopt for self-hosted if reserved.
Updated CTAssetsPickerController to 2.2.2, WordPress-iOS-Shared to 0.0.2, and WordPressCom-Stats-iOS to 0.0.2; Moved UIImage+Util category into shared pod.
moves NSUserDefaults keys to constants
adds string description for translators
Merge pull request #1832 from wordpress-mobile/issue/1829-mixpanel_opt_out

adds opt in setting for WPAnalytics
Updated import statement for UIImage+Util category.
Merge pull request #1834 from wordpress-mobile/feature/update-shared-pod

Updated WordPress-iOS-Shared,  WordPressCom-Stats-iOS, and  CTAssetsPickerController Cocoapods
Merge updates from develop