Make ResourceVersion a string internally instead of uint64

Allows us to define different watch versioning regimes in the future
as well as to encode information with the resource version.

This changes /watch/resources?resourceVersion=3 to start the watch at
4 instead of 3, which means clients can read a resource version and
then send it back to the server. Clients should no longer do math on
resource versions.

pkg/runtime/types.go

@@ -39,7 +39,7 @@ type TypeMeta struct {
 	ID                string    `json:"id,omitempty" yaml:"id,omitempty"`
 	CreationTimestamp util.Time `json:"creationTimestamp,omitempty" yaml:"creationTimestamp,omitempty"`
 	SelfLink          string    `json:"selfLink,omitempty" yaml:"selfLink,omitempty"`
-	ResourceVersion   uint64    `json:"resourceVersion,omitempty" yaml:"resourceVersion,omitempty"`
+	ResourceVersion   string    `json:"resourceVersion,omitempty" yaml:"resourceVersion,omitempty"`
 	APIVersion        string    `json:"apiVersion,omitempty" yaml:"apiVersion,omitempty"`
 }