Upload multiple files at once

## Gentics Mesh Version, operating system, or hardware.
- v1.4.2

## Operating System
- Linux
- MacOSX
- Windows
- Other, name?

## JVM
- Oracle JDK 1.8.0_100
- Open JDK 1.8.0_100

## Problem
You can't upload multiple files at once, you have to create a binary node for each file give it a name etc...
There should be a way to store all files in an assets folder, and bulk upload them, the binary node would be automatically created, and the name set from the file name.

## Reproducer

## Expected behaviour and actual behaviour

No files, tests, or entry points are identified in the issue. Start by locating the existing binary-node creation and upload API, then determine how an assets folder and multi-file request would fit the current model. Done means multiple files can be uploaded together, binary nodes are created automatically, and their names come from the file names.

Written by the indexing model from the issue text.