Support that some region selectable:false in geo.

### What problem does this feature solve?
When making a seatmap, some seats has been taken by others so they can not be selected.
It would be great to provide an option to support that some regions can not be selected but others can be selected.

### What does the proposed API look like?
```js
option = {
geo: {
// regions '1A' and '15B' can not be selected.
regions: [{
name: '1A',
selectable: false
}, {
name: '15B',
selectable: false
}
}
};
```