Update device_server branch

[MarceloSalazar]

There are quite many users who are running mDS locally.

The device_server branch has to be updated to fix/improve at least the following:

• Dependencies
• GW binaries
• Documentation (instructions, configurations, and supported features such as Thread router and Sleepy end-node)

[ciarmcom]

ARM Internal Ref: ONME-2491

[SeppoTakalo]

Commit https://github.com/ARMmbed/mbed-client-example-6lowpan/commit/2c070adec9fbabdb46d44d4477e9980f16a86e73 Updated the device_server branch.