Import is slow

import cirq takes around 1.5 seconds (this is in colab).

Would be nice to get some other numbers from users as to what they are seeing.

[vtomole]

Ubuntu 18.04

(venv3.6) vtomole@vtomole:~$ python -c 'import time; time.sleep(1); t1 = time.monotonic(); import cirq; t2 = time.monotonic(); print(t2-t1)'
4.911438770999666

[dabacon]

Using tuna, the top offenders are numpy, sympy, matplotlib, pandas, and networkx. We’ve added code #4653 to do LazyLoading for scipy which was also slow. The good news is that the problem is mostly these external deps, not cirq.