modify grid lines to be white rather than grey

[wkvong]

the grey grid lines make it difficult to click/edit the grey cells, if it's easy it might be worth changing them to another more visible colour like white, see training input grid below:

[aysjajohnson]

The only thing I wonder about is how intentional this was -- maybe there are some grids where this is important? I'll work on changing it for now, it should be pretty easy to revert in either case

[aysjajohnson]

[aysjajohnson]

this is how it now looks ^

[wkvong]

looks much better now!