package/python-channels: new package

package/python-channels: new package

Channels augments Django to bring WebSocket, long-poll HTTP, task
offloading and other async support to your code, using familiar Django
design patterns and a flexible underlying framework that lets you not
only customize behaviours but also write support for your own
protocols and needs.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
[Thomas:
 - alphabetic ordering of selects in Config.in
 - add missing BR2_PACKAGE_PYTHON3 dependency]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>