SINGA-482 tc comprehension integration

[dcslin]

Hi this is not completely ready for merge, pending to fix a testing error.

[dcslin]

Hi, this is the working version of tc integration for now, with following notes:

1. tested in the environment specified in the dockerfile cuda9
2. it implemented MatMul, Relu in TC for demonstration and usage is shown in following tests:
   ./bin/test_singa --gtest_filter=*TC*, and tests are passing.
3. for now only working in Cuda environment, and only working with type float

P.S. softmax is implemented but still checking why the output is not correct.

[dcslin]

TODO:

1. move tc execution code into device DoExec, and support CPU
2. package dependencies as conda package
3. integer support

[dcslin]

Integration is done except support CPU.
CPU support development is done, however the behavior was not expected even in clean TC env.
CPU backed TC return zero tensor as shown in https://gist.githubusercontent.com/dcslin/f3ed411012c144163f3bedbe621257f6/raw/9f6af3f5e62b5bb52a58c087967c813b3acd8872/tensor-comprehension-cpu-errors

[dcslin]

Ready for review.