Allow switching between big and small numbers easily

[ghost]

When adding small numbers, sometimes it becomes obvious that that number can only be in one box, and so I need to switch to big numbers, enter it, then back to small numbers to continue working through the puzzle.

I'd like to propose allowing to enter big numbers when in small numbers mode by long-pressing in a box, and vice versa. I think this will help make the app more user-friendly.

[luvarpt]

I would consider also double tap (or triple tap) for this action (use "big" number in mark mode).
Note, that this should go in line with future solution for #68 issue.

[annihat]

I would like either long-press or double-tap to toggle entry mode for one entry then toggle back.

For instance, if I've selected [3] to find all instances but spot a solitary 5 which shows up an 8, then a 1 I have to select [5] at the bottom, make the entry, select [8], then [1] then revert to [3] & if I do this for a few numbers I forget I was looking for 3 & my scheme of looking for numbers in succession goes awry.

@petermayer, just to be clear, I'm asking for a second but related enhancement here.