Enhancement(columnMenu) option to suppress removal of sort, #1603 #1604

Also fixes issue where column menu still displayed with a long press
even where column menu was disabled for that column.
Merge pull request #1627 from PaulL1/extend_column_menu_disabling

Enhancement(columnMenu) option to suppress removal of sort, #1603 #1604
Update README.md
Merge pull request #1638 from matthiasn/patch-1

Update README.md
Merge branch 'master' of https://github.com/angular-ui/ng-grid into move-columns
column movement logic added