nitdoc: improves quicksearch

Basic match is made on the begining of the string:
* first we select results with startsWith(substring)
* then we apply ranking using Dice coefficient
* rank bonus is given to exact match

If there is no match found:
* we rank all the entries and sort them
* entries with a Dice coefficient = 0 are trimmed

Also made some improvements on the GUI:
* results are grouped by name
* user can scroll the results list
* better handling of arrows in the search text field

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>