Update js/grid.common.js

add support of `editoptions.postData` and `ajaxSelectOptions.postData` for editing.
Merge pull request #404 from OlegKi/master

postData for building selects using dataUrl
Fix addRowData in case of array data and undeined rowid. Thanks to GeorgeG
Adding a displayField property in grouping in order to display it instead of default group Value. Thanks to Matthew Hutton