Fix: AWS s3 doc signature generation and upload

All params for upload file generation on server side. - Final file url, read write policy, signature

.env-sample: Added aws accesskey option
config.js: Added aws accesskey and bucket option
actions/aws_signature.js: Gnerate file name using timestamp and file url
lib/aws_signature.js: Optimize code for signature
public/js/controllers.js: fileNameChanged code optimize
public/js/services.js: Added service for generating signature and uploading file
public/views/pages/jobs-detail.html and public/views/pages/jobs.html : Removed Access key. Now access key and required params are get through 'AwsS3' services