freeze/thaw reactiveValues with namespace support

[schloerke]

The current definition of $.reactivevalues adds a namespace to the key. When freezing, the same namespaced-key needs to be frozen and thawed.

Current value of $.reactivevalues

`$.reactivevalues` <- function(x, name) {
  checkName(name)
  .subset2(x, 'impl')$get(.subset2(x, 'ns')(name))
}