Merge branch 'develop' of github.com:PaddlePaddle/VisualDL into feature/add_image_component-add_server_test

just a trick to store int8 in protobuf

should limit the maximum image shape latter

support onnx as graph data format and add related API

Merge branch 'feature/apply_frontend_travis_ci' of github.com:ChunweiYan/VisualDL-1 into feature/apply_frontend_travis_ci

* scalars frontend basically done

* frontend rename common/fun to util

* add images, scalar config

* add expandpael arrow

* fix scalars tooltip display problem

fix most bugs

waiting for frontend to fix interfaces

Update data format design

add graph data format design