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 
OK.  Here's the case.  
```
switch (n)
    case 1:
        echo 1;
```

Since switch has the alternative syntax
```
switch (n):
    case 1:
        break;
endswitch;
```

The ```$startSwitchIndex``` may land on the ```:``` after ```case```.

I agree -3 is a WAG.  I should use ```getPrevNonWhitespace``` instead.  Let me fix this up.