Support Ctrl-A select all rows in grid

[pauldelano]

ag-Grid supports keyboard shortcuts like Ctrl-C Copy but not Ctrl-A Select-all.

It can be implemented in an application by adding a grid keyDown event handler:

keyDown(evt) {
  if (evt.ctrlKey && evt.key == 'a') {
    gridModel.agAPi.selectAllFiltered();
  }
}

See related selModel issue #1150.

[lbwexler]

I took this and implemented it here, but am finding that our selModel's attempt to do selectAll() is still unbelievably slow. I thought we fixed this?

UPDATE: The selection fixes works great -- had somehow not pulled the new code locally