Optimize library update thread

[Petr Nejedly]

Look if it would be possible to record all changes (new, updated,removed) files during one cycle of going through all the files.

ATM it goes through it 3 times.

[Petr Nejedly]

Issue #61 was marked as a duplicate of this issue.

[Petr Nejedly]

- Try splitting update thread into add and update threads, add running more often. - Look into caching all existing files from DB with their modified date during first update and check against that in subsequent updates

[Petr Nejedly]

also look at CPU utilization: http://stackoverflow.com/questions/464387/is-it-possible-to-control-cpu-usage-from-a-java-application

[Petr Nejedly]

Removing version: 0.4 (automated comment)