Strategic Form and Matrix Layout merged into a single tab

[stengel]

Strategic form input should only be an input mode in the strategic form.
That is, we only want 2 tabs not 3 as now:

The strategic form tab on the left should be the current matrix layout with (and this is the new thing) clickable entries.

Behavior:
Clicking on a single payoff only allows change of that payoff.

Clicking anywhere else in the cell pops up both payoffs separated by blanks.
Typing overwrites like on spreadsheet input (i.e. no highlight and delete necessary).
If only one number is input then the second number is left unchanged, or taken as the negative for zero-sum input.

Special keys when entering data: All the following conclude data entry, except for Esc which cancels:

• Enter requires new clicking.
• Tab goes to the next cell.
• Shift-Tab goes to the previous cell.
• Arrow-down and arrow-up (analogous to Tab and Shift-Tab) conclude entry and go to the cell below or above.
• These do not terminate entry: Arrow-left and arrow-right navigate inside the cell.