Package installation options

[sarahmish]

As the number of pipelines in Orion grows, we most likely require additional dependencies. In some cases, pipelines are stored for benchmarking purposes (for example, azure). Sometimes, these packages are large and take an exceeding amount of time in pip installations and testing. In order to scale down the number of packages needed, we can create an option for what type of orion installation is required.

I'm proposing two optional dependencies. Orion for using OrionExplorer and another one for using benchmarking pipelines. Something close to pip install orion[db] and pip install orion[bench]. One challenge here is, bench refers to benchmark pipelines and not the benchmark utility which should be available in all cases.

Required changes in setup.py

db_requires = [
    'mongoengine>=0.16.3,<0.17', 
    'pymongo>=3.7.2,<4'
]

bench_requires = [
    'azure-cognitiveservices-anomalydetector>=0.3,<0.4'
]

extras_require={
    'test': tests_require,
    'dev': development_requires + tests_require,
    'db': db_requires,
    'bench': bench_requires,
    'complete': db_requires + bench_requires # install everything
}

This issue is inspired by #181.