Support for singleton constructor functions

The service manager now keeps track of instances of singleton implementations
(i.e., implementations whose XML description lists at least one
<singleton ...>).  These instances will be disposed either when the service
manager is disposed, or, for instances that have been instantiated into the
component context's /singleton/* map, when the component context is disposed.

This change allows to use constructor functions for such singleton
implementations, too.

Change-Id: I220c9ddc9824e4d7f7556daefb599e2ec36b0e6c
Introduce com.sun.star.frame.theGlobalEventBroadcaster singleton

...to supersede com.sun.star.frame.GlobalEventBroadcaster single-instance
service.

Change-Id: I74ecaadadb4c600d39979aa7c13b6389bed38fd7
Revert "Revert "sfx: Use constructor feature for SfxGlobalEvents_Impl.""

This reverts commit ef37781683e28d1837cfce86de990e59d2c10c5f, now that
constructor function support for singleton implementations is in place and the
proper singleton theGlobalEventBroadcaster has been introduced (and drops
sfx_component_getFactory completely, which had become unused except for
SfxGlobalEvents_Impl in the meantime).

Change-Id: I2d587989dd0a1fbea6fe75f7dc2af954ac81c4ed
Assert SwReaderWriter::GetReader returning non-null

...happened to fail for me once, for unclear reasons.

Change-Id: Idf88ff4952924a814e465b039fbae384691ba7a6