[SES-2018] Refactor mention (#1510)

* Refactor mention

* Fixes robolectric test problem

* Fixes tests

* Naming and comments

* Naming

* Dispatcher

---------

Co-authored-by: fanchao <git@fanchao.dev>

libsession/src/main/java/org/session/libsession/messaging/open_groups/GroupMember.kt

@@ -6,6 +6,11 @@ data class GroupMember(
     val role: GroupMemberRole
 )
 
-enum class GroupMemberRole {
-    STANDARD, ZOOMBIE, MODERATOR, ADMIN, HIDDEN_MODERATOR, HIDDEN_ADMIN
+enum class GroupMemberRole(val isModerator: Boolean = false) {
+    STANDARD,
+    ZOOMBIE,
+    MODERATOR(true),
+    ADMIN(true),
+    HIDDEN_MODERATOR(true),
+    HIDDEN_ADMIN(true),
 }