Added console command and report widget to clear images cache

[PubliAlex]

This PR provide 2 methods to clear cache of images.

• A new console command : php artisan responsive-images:clear
• A new report widget with a button that trigger the above artisan command.

This new command do 2 things to clear images cache :

• Clean the storage/app/resources/resize folder where image resized by the core Resizer class are located
• Clean all images with prefix "img_" located in storage/temp/public where this plugin stock the responsive images.

This PR fix this issue #64

[tobias-kuendig]

Thank you, @PubliAlex! This has been merged in 86438b18829ae7be8d3235f294486347d6457c27 and is released as v2.5.1.