Refactoring Utils

This removes duplication regarding the `calculateIndent` function, adds missing docblocks, and adds tests for the `calculateIndent` function too.
Yeah, my code wasn't token but string - perfectly valid for current interface.
I am totally for changing interface to Token.
I, personally, do sth like 
```php
public static function TokensAnalyzer::calculateWhitespaceTrailingIndent(Token $token)
{
    if (!$token->isComment()) {
        throw ...
    }

    return ....
}
```

but it is just a first thought, need rethink