New validators for input type file. 

Useful when multiple attribute enable.

New options:
- maxFiles: The maximum number of files
- minFiles: The minimum number of files
- maxTotalSize: The maximum size in bytes for all files
- minTotalSize: The minimum size in bytes for all files

Example: max 5 files

 <input type="file" class="form-control" name="attachments" data-bv-file-maxfiles="5" multiple />