Import data streams - reuse infrastructure for ScAreaLink.

Change-Id: I18db991d2e8e665d5e4ca778344993e79772ccd5
export data streams; pretend to be an area link

Fix ScXMLExport::GetAreaLinks to not use UNO, so we can hack DataStreams
into ScMyAreaLinksContainer.
We need to connect them to cells for export / import - that does not make
sense for DataStream without any attached range. We use an arbitrary one.
But you might remove it, if you create another ScAreaLink / DataStream
with the same range, without knowing about it.

Maybe it wouldn't be that bad to let DataStream inherit from ScAreaLink.

Change-Id: I5b85a9329ba1ca46fb2893b54fe5161d2fb22f47
Allow to edit data stream from Edit-> Links... dialog.

Change-Id: Ibb456da55f04c39ddb7b58eb71ca488cf209edb5
datastreams: for security, ask before executing a script when importing

Change-Id: Ia6e4cb911958e903afa3abf7ccb0f1a163a97a65
Let's use ScRefreshTimer for data streams instead of our own thread.

As was the original idea, for some reason abandoned, and as ScAreaLink does.

The main advantage is that ImportData() is not called anymore with
invalid mpScDocument (when we close it).
There is surely something going on with SolarMutex and it just works better.

Change-Id: I09256a18ffa14606fc8e06b968016bbc0562a6fa