Allow to edit data stream from Edit-> Links... dialog.

Change-Id: Ibb456da55f04c39ddb7b58eb71ca488cf209edb5
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.
We do not need to use our own SolarMutexGuard.

Change-Id: I09256a18ffa14606fc8e06b968016bbc0562a6fa
datastreams: for security, ask before executing a script when importing

Change-Id: I76a11dae2569eb7e0c791c9f1fb20626c4ff7528
datastreams: Simplify code for importing CSV data.

The code is copied and simplified from sc/source/ui/docshell/impex.cxx.

Change-Id: I15a426a16c4f2ba659af86492c1b2e4ba879d8b6
datastreams: No need to disable undo. We do not add undo actions.

Also fixes memory leak, because EnableUndo()
was called from Document's destructor.

Change-Id: I637ff62bde6f8c3238238323e6e4a5a5d2b81881
fix memory leak

Change-Id: Ic84ace8ac3aa52009f43aafe78283730f97881f2