Make NameableGraph optionally editable
Make NameableGraph optionally editable

This allows the renameability of NameableGraph to be controlled by the
presence of any one of the editing handler functions. Since we don't
pass any of these when rendering a HostPage, those graphs will have
static names, and will prevent the user from editing the names of those
graphs to no avail. Also, because the handlers were marked required, it
caused the HostPage to entirely break, which is fixed by this commit.

brianbaker/chronograf,brianbaker/chronograf,brianbaker/chronograf,brianbaker/chronograf,brianbaker/chronograf