buildroot

python-flask: bump to version 0.11

Change download location and rework dependencies, i.e.
select Python's zlib support and python-click package
and remove unneeded build-time dependencies.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>