Improved experimental /termfreq operation.

Limiting the number of results returned makes this operation
significantly faster. Pass 'first' and 'number' parameters to determine
which term frequencies to return.

You can also pass 'property' (i.e. word, lemma, pos) and 'sensitive'
(yes, no) to determine what frequencies you would like to calculate.

Also added bounds checking to first and number parameters and added the
maxPageSize configuration setting.