Service Box widgets improvements.

Changes on widgets:

* PrintSnapshot
* KMLFileUploadPanel
* MapFileUploadPanel

in order to include the error log from servicebox.

Also include:

* PrintSnapshot --> Add SERVICE=WMS to the request URL.
* MapFileDownloadPanel --> Hide load mask when the request fails.

This changes and the geosolutions-it/servicebox#5 pull request fixes #138 issue.
Merge pull request #302 from alediator/issue_138_servicebox_improvements

Service Box widgets improvements.