first implementation of threeStateSort:true option
first implementation of threeStateSort:true option

The option can be used in standard sorting mode (`multiSort: false`). It
changes the default two state sorting behavior of column sorting
(asc/desc) to three state behavior (asc/desc/no sorting). We use now
`lso` property (abbreviation of Last Sort Order) of colModel items in
the same way like in case of multisort. The current code seems to work
correctly. It will be later rewritten to remove `multiSort` function and
to implement all inside of `sortData`. The optimized code will be posted
later.

javapark/jqgrid