CORE-4167 Fix for Sessions loading at start-up.

Sessions were loading even when users had Sessions disabled.
The user's Sessions-enabled flag is fetched from the user's Preferences.
Moved the getUserSession call in DEPresenter from the initializeUserInfoAttributes method into the loadPreferences method.
Moved the loadPreferences method to a more logical part of the file.
CORE-2925 Refactored Intro dialog box in DEPresenter.

Renamed parseWorkspaceId to parseWorkspaceInfo, since it also parses the "isNewUser" flag for the UserInfo object.
Refactored the "Welcome" confirmation box into an initIntro method.
Called this method from parseWorkspaceInfo, since this is where the "isNewUser" flag is parsed.