Fix #1431 "Grid menu is cropped in scrolling dialogs"

- don't move global menus in DOM, but with CSS
- fix menu z-index
- move grid/repeater JS files to XBL
Client-side test for fr:grid menu

- operate the menu a bit and make sure it opens, closes, and activate choices
- see also #1431
Remove fr:datatable (deprecated since 4.0)
Fix #1492 "Repeat menu does not show if resources are not combined"
fr:grid menu: test iteration removal

- see also #1431
Fix #1550 "Error moving iteration with autocomplete in repeat"

- ignore "nested refreshes" as they are not allowed
- set requireRefresh = false at beginning of refresh as that's more correct if a refresh is caused by events
- some refactoring
Relative paths for checkbox images
Return 403 if no auth based on roles, fix #1382
Use output instead of group, fix #1580
Test for #1550
Fix #1579 "Move iteration in new nested repeat causes JS error"

- server is now able to send repeat hierarchy updates to the client
- only do this if there is at least one xxf:dynamic control
- use xxf:load with a javascript: scheme
Fix #1578 "Itemset editor doesn't always show list of languages"
Fix extra value in grid header