Production push: search nearby members, link to gravatar on settings page, other small tweaks

1) Search nearby members -- more work still needed, but a basic search is there.
2) Link to gravatar on member settings page, to make it easy to change your avatar
3) Switch location of sign up/sign in, so that sign in is in the same place as sign out was when you just clicked it
4) Bugfix: make sender name clickable on notifications index page