cleanups/improvements to spec and code:

- move /settings/pacUrl to /connectivity/pacUrl
- rename "gtalkConnecting" modal to "connecting"
- ditch /connectivity/lanternController. instead use
  /connectivity/connectingStatus to allow the frontend to display an arbitrary
  message describing Lantern's progress during the connection process. the
  ui and mock backend now use this for the "connecting" modal.
- spec changes to /version:
  - replace /version/latest/changes with /version/latest/infoUrl
  - /version/installed needs no "installerSHA1" or "infoUrl" field,
    only /version/latest does
  - consolidate separate "modelSchema" and "api" version fields into
    just "api", which encompasses the state document schema, update protocol,
    and http api
  - /version/latest needs no "api" field, only /version/installed does, as it's
    only used by the currently running backend to tell the frontend what
    version it conforms to
- remove modal types that will not be in this release from the spec
- comment out html for requestInvite and inviteSent modals
- disable submitting scenarios form (at least for now)
- remove unused update-on-blur directive
- style tweaks