Avatar: Refactor some code, allow set avatar from server for FS and GridFS

lib/fileUpload.js

...rocketchat-file-upload/client/lib/FileUploadFileSystem.js

...hat-file-upload/server/config/configFileUploadAmazonS3.js

...t-file-upload/server/config/configFileUploadFileSystem.js

...ile-upload/server/config/configFileUploadGoogleStorage.js

...tchat-file-upload/server/config/configFileUploadGridFS.js

packages/rocketchat-file-upload/server/lib/FileUpload.js

packages/rocketchat-lib/server/functions/deleteMessage.js

packages/rocketchat-lib/server/functions/deleteUser.js

packages/rocketchat-lib/server/functions/setUserAvatar.js

server/methods/deleteFileMessage.js

server/methods/resetAvatar.js

server/startup/initialData.js