Adds a home for viewing and editing user preferences at a new client
route: /settings/. This is first in a series of changes to bring
preferences editing to PolyGerrit. At this point the settings page is
read-only and mostly un-styled.
Introduces the gr-settings-view element which is added to gr-app in the
same manner as the other main PolyGerrit views. Introduces the /settings
route which will display the new view, or redirect to login if the user
is not authenticated. Adds a link to user settings in the
gr-account-dropdown.
Bug: Issue 3911
Change-Id: Ib164502d586518876737c6d333c8940f2898dad4
60ea95fac7