add a function to script context to get principals email address.

There should be a function called GetEmailFromPrincipals (varname) where varname is a list of strings. the type of varname should be compatible with what returns operation "Get principals for permission"
GetEmailFromPrincipals returns a list of strings.

When principal is a group, it should resolve emails of all the members of the group. When member's email is null, it should not be added as an element to the list.