Added Searcher.openForwardIndices() method to open all
forward indices at once.

Forward indices are normally only opened when needed, but this may cause
unpredictable slowdowns. This method allows you to open all forward
indices as you start the application. This may take a while though.

In QueryTool, the new "openfi" command calls this method.
Added performance test utilities.

* added BatchContentStore, -ForwardIndex and -LuceneIndex to performance
test parts separately.
* fixed bug with HitsWindow not keeping the correct value of
totalNumberOfHits.
* added some commands to QueryTool for testing stuff.