add another parameter( isByArrowKey) to differenciate if the focus is
made by arrow key
Merge pull request #263 from shanghaikid/addAnotherParamToDiffByKey

add another parameter( isByArrowKey) to differentiate if the focus is
Merge branch 'master' of https://github.com/oria/gridx into serverSelectionOptimization
* add an api: getIdByVisualId, now you can use it in the selection modules
to get better performance
* make build selection cache more robust