use yapf to format python code, add style config file

Add checkout name for Dockerfile

Feature/fix pydataprovider multiple obj bugs

* Fix #436

fix test_layerHelpers unittest error

add SpatialPyramidPoolLayer c++ support

Fix previous ci error.

change the act.name for LinearActivation() to "linear" so that it won't fail in hl_activetype; also fix the hasinputsset in submodel

Add SumCost

'*' operator overload for LayerOutput

Making '*' support the multiplication between a scalar and LayerOutput

Also changing '+' to support adding between a vector and a scalar.

Change-Id: I7daf35590dc2b2f855a29d9ef43ac57979442e0f

* Because in dockerhub, we cannot set the `docker build `running
  directory, we could only use `git clone` command to get the latest
  code if we put `Dockerfile` in subdirectory

* But the `git clone` will checkout the default branch only, so here
  we add a `ENV` in Dockerfile to checkout special branch or tag in
  git repo. We could change it to `V0.9.0` tag when it release.

Add bilinear interpolation layer

fail in hl_activetype; also fix the hasinputsset in submodel

* set mixedlayer output size according to input operator
* change from num_channel to num_channels for conv_operator (the old one is
really misleading because all the others are num_channels)

* also changed the arg name in projections.py

Fix matrix inverse  unittest to be more robust