Python API changes

Frame -> H2OFrame
Cluster -> H2OConnection
Global default connection
Local/remote files & data distinction
"Safe" REST (unified REST error check)
First rapids call attempt
Some more rapids/python

vec+scalar remotely
Some accessors
More interaction with remote Frame

Fetch basic info (#rows), cutouts for mixing data between local &
remote.  Prep work for printing head of remote frame locally.
fix javac warnings
Support delete of vecs from python

...in progress for printing datasets on cluster in python...
Progress with python API

Parse supports "delete Frame keep Vecs" flag, which returns all the Vec
keys.
Parse returns the rows parsed also.
Rapids supports single-Vecs as a 1-col Frame
Rapids uses '%' instead of '$' for marking IDs; modulus uses 'mod'
instead of '%'
Big Data math happening, wrestling with getting the results back to
Python
Merge branch 'master' into cliffc-py

Conflicts:
	h2o-core/src/main/java/water/api/RemoveHandler.java
Flip $ for % in tests
Merge branch 'master' of github.com:h2oai/h2o-dev

Conflicts:
	h2o-core/src/main/java/water/rapids/AST.java
	h2o-core/src/main/java/water/rapids/Exec.java
Merge branch 'master' of github.com:h2oai/h2o-dev
Merge branch 'master' of github.com:h2oai/h2o-dev