This is a preparation change for replacing of AccountGeneralPreferences
entity with git backend. GET and PUT REST handlers for user preferences
accept and return MyMenu instances and store/read them to/from the git
backend. This is why this class wasn't added to
AccountGeneralPreferences that represents db backend. Now, that we are
moving all preferences to git backend it makes sense to keep all
attributes in one class. This location is the client package in
gerrit-extension project, as they must be part of GWT modulde.
Change-Id: I5b879c4fa690efa31976b5d65a31adbcc3f7a37c
3f838ae80f