kanjipad extension: add prediction mode

```
User should be able to activate an alternative prediction matching mode, which 
may be slower than the default mode but it may find kanjis which the user may 
draw with the next one or two strokes.
In aedict3 this should be represented by a simple check box.
```

Original issue reported on code.google.com by `martin.v...@gmail.com` on 20 Dec 2014 at 10:35
