Patch for clear method

Patch for the issue about Clear() method, please refer to [#2](https://github.com/JN-Jones/visitor-log/issues/2)

### What has been changed ?

* Added a parameter into the config.php called `datetype`, it has two options : 
  * `timestamps` - If the user is actually using **TRUE** timestamps, he has to switch to this the `datetype`
  * `date`- If the user is using complete datetime, it's the default option as Laravel isn't using timestamps with Carbon API on the 4.2, 4.1 and neither on the 4.0 but the user can switch to timestamps.
* Added a check in the clear method, it will change the delete method depending on what type of date is currently using the user.