Serializing lots of scanned files blocks gui for a long time

After scanning directory with a lot of files (~50k) the scanned files information is being stored in the sqlite database as single transaction commit.
This commit is being done in a main/GUI thread (within OnTimer() handler).
There are also other places where this kind of blocking can occur, but this one seems to be causing the most trouble right now.

Most probably transaction commit should be moved to a separate thread - this needs a test on release version of CH.