Modify CFT to allow for Multiple IAMUsers and Multiple ManagedAccounts

[danbryan]

IAMAccount.template

• Change IAMUser to IAMUsers, with type CommaDelimitedList
• Change ManagedAccount to ManagedAccounts, with type CommaDelimitedList
• Change addUserToGroup to add each user defined in IAMUsers to the Group.
• Change MacGroup PolicyDocument to add one Policy Statement Resource for each Managed Account

If this can not be done in native CFT, then create a Lambda Job to take the IAMUsers, and ManagedAccounts as payload, and return the proper CFT syntax that can be substituted in.