grid control should have some sort of update button

[jasongrout]

Almost every time we update a matrix using the InputGrid control, we want to make updates to multiple fields and then send it to the interact. In Sage Cloud William implemented a little green checkbox next to the input grid which would send the grid contents to the interact, and this is incredibly convenient (and small; not having the word "update" seems nice). Here's a proposal for changing our input grid control:

• Make some sort of small little button or something off to the side, and don't submit the grid contents until the button is pushed
• Make each input outlined in the dirty style as it is changed (so it's easy to see which entries of the matrix have been modified

[kcrisman]

See #450 - the matrix input (easy version) doesn't work at all now, at least not in the way it does in sagenb and cloud. (Incidentally, the checkbox in cloud is not at all obvious in intent, like so many things there...)