Improvement: Allow the user to adjust the size of a square before accepting it

[trev33b]

Sometimes it can be really hard to click in the exact right place to make the square as perfectly sized as possible.

As a suggestion, after the user has drawn their square, don't immediate calculate the grid size. Instead, show a square on the screen with resize handles so the user can adjust the square size.

This could be useful when working with a hand-written map or when trying to convert a map from say 10' squares to 5' squares and you are having trouble finding a good average point. (Note: My other suggestion with allowing the user to enter the number of rows/columns should really cover that case, so that's less important for this issue).

This might be a low priority item if you implement my other suggestion to enter multiple squares on the map.