Merge branch 'cyphers/autodiff' of https://github.com/NervanaSystems/private-ngraph-cpp into cyphers/autodiff

Merge branch 'cyphers/autodiff' of https://github.com/NervanaSystems/private-ngraph-cpp into cyphers/autodiff

change all passes to take shared_ptr rather than naked pointer

missing include

fixing vector length

format fixes

avoid repeating input values in a test

use input

trig/hyper funcs

* Formatting; fix erroneous "type_prop" classification for reduce and slice tests

* Clarify comment

* Add step parameter to slice, with type checking but not (yet) implementation in VM

* Add elementwise exp to VM

* Formatting

Bob/warnings

* Type checking for reshape op

* Formatting

* Implement reduce op for matrices and smaller in VM

* Formatting

* Missing include for Ubuntu

* Remove IndexBuiltin class

Docker: Add more deps

Add a minimal Backend API and make the interpreter use it.
read/write tensors (for frameworks)

* cleanup

* fix node includes

Moved all apt-get install commands into same RUN line as apt-get update.  There is a subtle timebomb if apt-get update is performed in a separate RUN line, due to how docker layers work. (#179)

* isolate graph building / execution scope in some unit tests (this triggered the user-after-free which was also observed from TF)

* Change descriptor::layout::TensorViewLayout to store a shared pointer to the TensorViewType rather than a reference to the TensorView

* port functions from funky passman branch

* update pass tests

* wip

* fixed

* remove obsolete test

* remove debug prints

Include cmath for 'expf' etc.