Added SwitchCaseFixer - first draft.

This is to fix #776.  It's my first attempt at creating a fixer modeled from BracesFixer. Please critique away.  Thanks.

I will be adding a test case for the alternative switch syntax.  This fixer will fail that case currently.
```
switch (n):
    case 1:
        echo 1;
        break;
    default:
        echo n;
endswitch;
```

Ping @keradus @gimler
// cc @GrahamCampbell @stof @sstok 
spaces around `-`.
why -3 ? what is that offset? it looks risky