Update import paths after move from tools repo

Also:
- Move the watcher to cmd/watcher (somehow this was missed earlier).
- Move dashboard package from the repo root to its own directory.
- Update docker build scripts. (Although not yet the version hashes in
  the Dockerfiles; this leaves the docker builds broken, but they were
  already broken after moving the builder to cmd/builder. They'll be
  fixed in a followup CL after this one is submitted.)

Change-Id: I29a9758da1f3c60446e3ce18174c0df26e4d8325
Reviewed-on: https://go-review.googlesource.com/3077
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/buildlet/buildletclient.go b/buildlet/buildletclient.go
index 53b2c6a..4d1e2c1 100644
--- a/buildlet/buildletclient.go
+++ b/buildlet/buildletclient.go
@@ -6,7 +6,7 @@
 
 // Package buildlet contains client tools for working with a buildlet
 // server.
-package buildlet // import "golang.org/x/tools/dashboard/buildlet"
+package buildlet // import "golang.org/x/build/buildlet"
 
 import (
 	"errors"