add default palceholder picture for non image types

[hosseinjalili]

hi

please add an ability to add a json file for non image file picture placeholder like .pdf. for example: <ng2-file-input (onAction)="fileChange($event)" [typePlaceHolder]="{'.pdf':data:image/png;base64,iVBORw0KGg}" extensions="['jpeg','png','jpg','pdf']">

then base64 image place on src img tag attribute and show that image and title beside each other.

regards