Added upload multiple images from local storage feature

[ganeshsp1]

Added an option to upload multiple images from the gallery, such that the user can click images before hand and upload them all together. The images will be uploaded in the background.

UI Change : New FloatingActionButton to Upload Images. New Pub dependency Added :multi_media_picker - to select and upload multiple images. Code Change has been integrated in the camera.dart file to resuse the code for uploading images to firebase storage

[ganeshsp1]

Updated Readme to correct service_account_key.json file name to service-account-key.json since the former causes an exception while uploading videos { Error: ENOENT: no such file or directory, open '/srv/lib/service-account-key.json' errno: -2, code: 'ENOENT', syscall: 'open', path: '/srv/lib/service-account-key.json' }

Hence found that the correct file name should be service-account-key.json as opposed to what was mentioned in the readme. Also this caused other issues since the video was not converted, but still the number of images was updated and showed incorrect numbers.

[ganeshsp1]

Please find the screenshots for the Multiple Image Upload Feature

Image 1

Image 2

Image 3

Image 4

[Eyesonly88]

Hi there, this is a very useful PR, can someone please merge it?

[Eyesonly88]

@prakhar1989 @ganeshsp1