Unblacklist group-specific JS/CSS for the user group

Changes ResourceLoaderUserGroupsModule so that if the
user is in the 'user' group, i.e., the user is not
anonymous, then custom JS or CSS can be inserted using
system messages in the same way as is allowed for other
user groups.

Bug: 47812
Change-Id: I0ef9674e1a9e1e5db9537ba7b9578d2b7b14fd8e
Merge "Unblacklist group-specific JS/CSS for the user group"