Add a reload() function for datagrids.

This adds a reload() function that can be called on a datagrid element.
It will trigger a dynamic reload of the grid using the server-side
settings.

Tested column toggling and reordering.

Temporarily set a global variable to point to the datagrid and called
reload() on it, after tweaking stuff on the grid in another tab.
The grid reloaded and I saw the new version of it.