PIVOT-947:  Add hooks to VFS Browser dialog to add components.

* Add two methods to the TerraVFSBrowserSheetSkin:
  . "addLabelComponent"
  . "getBrowser"
* Implement "addLabelComponent" there by adding the component to the "hostNameBoxPane".
* Add new constructor to VFSBrowserSheet to take FileObject values instead of Strings.
* Extend the VFSBrowser.Skin interface to add an "addActionComponent" method and implement
  it by deferring to the real skin.
* Make the button BoxPane accessible to the TerraVFSBrowserSkin from the bxml and implement
  "addActionComponent" by adding the new component there.


git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1591089 13f79535-47bb-0310-9956-ffa450edef68