allow importing when cursor is at beginning of symbol

previously, when ctrl + opt + i  is pressed while the cursor is just before the class name you want to import, e.g. 

```
Foo myFoo = [ Foo new ];
//           ^ cursor is here
```

the cedar short cuts would import "null.h" which is obviously wrong. Now the short cut adds "Foo.h"

We couldn't find a better way to determine when to look forward for a symbol. It is possible that this code could be improved further.