More text window padding

These were some hardcoded values that were missed last time. They are used specifically to calculate sizes of text windows when used to present dialogue options. I also included padding calculations here where there previously were none:

```
int txoffs=0,tyoffs=0,yspos = scrnhit/2-(2*padding+needheight)/2;
```

Using a fresh copy of 3.3.0, I was able to verify that text windows for dialogue options were off vertically by 3 pixels. This wasn't so bad for fixed padding, but a padding value of 20 makes this really obvious.