update raco submodule
put up a warning when the user isn't using Chrome

fix #178
@domoritz' suggested fixes
remove unused jumbotron css
make phytoplankton demo use smaller data

Seconds, rather than minutes
vain attempt to get travis to work with google app engine again

Something is busted in Travis. I'm following this patch:

https://github.com/raphaelcuba/fbsdk-webapp2/commit/99bf7fd93b1808bf81b95244c99744073d37e9f0
switch GAE version to 1.81, the web standard
Merge pull request #180 from uwescience/detect-chrome

Detect chrome, warn if other browsers
Update README.md
raco: update submodule
editor: use POST not GET for any API call that passes query

Stupid 2000 character limit is stupid.

Fix #181
editor: implement per-language history

Basically, just change the content and history local storage objects from
being string/history to being dict[language] = string/history.

I also thus disabled the feature that always clicks the first example
when we change languages.

I also tried to make sure we get the correct behavior when the user
loads the page with no state, or with the old state.

Refer #179
editor: when empty physical plan, also disable rerender

Every time we switched to the tab, it would call re-render which would
show the old, outdated plan.
editor: remove keypress resetting

I forget now why we had this in the past, and I couldn't figure
out why in 5 minutes of playing. Maybe something else we've
re-designed has fixed it. In any case, I don't want pressing
space or arrow keys to reset the parsed plan, etc.
editor: refactor editor state

Condense the content/history into a single dictionary.
Refactor the editor-changing/language-changing/example-loading code.
Result: lose ~75 lines of code (127->51).

[Of course my prior patch may have added that many.]
restore language dropdown
Merge pull request #182 from uwescience/production

fix #181
Merge pull request #183 from uwescience/implement-editor-history

Implement editor history
update raco with backwards-incompatible aggregate format
myria-python: update submodule with backend SSL support