In gvedit, replaced `toAscii()` with `toLatin()`

In gvedit, replaced `toAscii()` with `toLatin()`

From the Qt documentation
(http://wiki.qt.io/Transition_from_Qt_4.x_to_Qt5#toAscii.28.29_and_fromAscii.28.29_Methods_are_deprecated):

toAscii() and fromAscii() Methods are deprecated

Replace all instances of

```
fromAscii()
toAscii()
```

to

```
fromLatin1()
toLatin1()
```