Implement range search for characters

Use the projection algorithm described by Bentley in "A SURVEY OF
TECHNIQUES FOR FIXED RADIUS NEAR NEIGHBOR SEARCHING" (1975) to speed up
the search of characters in a given range below O(n).

Link: http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-186.pdf
Merge branch 'testserver' into range_search
Update position in search structure properly
Fix test with characters
Fix some issues with range search

More than one character can be on the same field, use multimap.
Remove unused method getCharacterID.
Clear position container in central clear method.