Loads up profile summary info for the specified member and sets up $context stuff for the template.

• Called from ModifyProfile
• Usually accessed from ?action=profile or ?action=profile;u={user_id} since this is the first sub-action that most users can see
• Specifically accessed by appending ;sa=summary to one of the above querystrings
• Loads the member context and theme data
• Calculates the member's age based on their birthday if they've entered one
• Calculates the "posts per day" statistic based on how many posts the member has made and how long they've been registered