Set HIDDEN attribute on .Sugar-Metadata directory

According to the OLPC AU dpeloyment [1], 50% of the support calls they
get from teachers are due to a confusion caused by looking in the
.Sugar-Metadata directory for files from Windows. "On Windows, the
directory is not hidden, and people are going into it expecting their
files to be in there. What's even more confusing is that the filenames
they are looking for are indeed inside, but those are metadata and not
the actual files."

This patch uses a new Sugar extension, sugar-fatattr, to set the
HIDDEN attribute on the .Sugar-Metadata directory.[2]

[1] http://sugardextrose.org/issues/1367
[2] sugarlabs/sugar-toolkit-gtk3#33
Add online service support

This patch adds a new section to sugar/src/jarabe to manage web services.

The relevant feature request is [1].

Adds a new web section of jarabe is for a prototype of a new online
account management class that manages the services described above.
The services themselves are intended to be kept in subdirectors of
sugar/extensions/web and are the subject of a separate patch. Also
in a separate patch will be a UI extention to the Journal toolbar and
palette, adding new menuitems.

(Includes a unit test)

[1] http://wiki.sugarlabs.org/go/Features/Web_services