Handle blocked status of TM correctly for TM(X) export and other

So far a tmx export had been blocking the complete t5memory.

With the linked T5TMS-Issue Orest is making the TMX export run in a thread.

Yet still other requests to the currently exported memory will not be possible.

Therefore we have to block the TM from being used for fuzzy query, in analysis and for other TM-exports as long as the export is running.

The same should be true for TMX imports into a memory (which should already be implemented, but please check again, if it works correctly).

Please coordinate the way the status works with Orest.