Fix various bugs in the moderation feature. (#2608)

* Fix search field string.

* Show your own user as an Admin when changing roles.

* Also show invited users when changing roles.

* Don't allow admin's to kick/ban other admins or themselves.

* Fix a bug when left members were counted as admins/moderators.

* Show when a member is pending.

* Add sections to the change role screen.

ElementX/Sources/Mocks/RoomMemberProxyMock.swift

@@ -53,7 +53,7 @@ extension RoomMemberProxyMock {
     
     static var mockMeAdmin: RoomMemberProxyMock {
         RoomMemberProxyMock(with: .init(userID: "@me:matrix.org",
-                                        displayName: "Me admin",
+                                        displayName: "Me",
                                         avatarURL: URL.picturesDirectory,
                                         membership: .join,
                                         powerLevel: 100,