expose profiling in a limited way

[bmyerz]

• TODO (myria demo currently down) test with the following program

from myria import *
import numpy
connection = MyriaConnection(
   rest_url='http://demo.myria.cs.washington.edu:8753')
connection.execute_program("""T1 = scan(TwitterK);
 T2 = select * from T1;
 store(T2, JustX);""", profile=True)

[bmyerz]

all right appears to work
http://demo.myria.cs.washington.edu/profile?queryId=692

[BrandonHaynes]

Execution is now deferred to RACO, so will need to add the profile flag to the MyriaConnection class there before merging.