Fixes #464 (shapes not deleted when clearing all shapes)

[n-riesco]

• Reverted f67ff4d
• Added comment to the code
• Added test

Fixes #464

[etpinard]

@n-riesco Thanks for taking this on!

Looks your patch broke all non-cartesian plots. Let me know if you need help debugging this.

[n-riesco]

@etpinard Oh! I see what the problem is. fullLayout._subplotShapeLayer is undefined for non-cartesian plots. I'll fix it.

[n-riesco]

This time I run all the tests locally. The only one that fails, also fails in master:

user@host:~/github/plotly.js$ npm run test-jasmine

> plotly.js@1.9.0 test-jasmine /home/user/github/plotly.js
> karma start test/jasmine/karma.conf.js

22 04 2016 15:09:20.658:INFO [framework.browserify]: registering rebuild (autoWatch=true)
22 04 2016 15:09:29.664:INFO [framework.browserify]: 9097683 bytes written (8.21 seconds)
22 04 2016 15:09:29.825:INFO [framework.browserify]: bundle built
22 04 2016 15:09:29.847:WARN [karma]: No captured browser, open http://localhost:9876/
22 04 2016 15:09:29.852:INFO [karma]: Karma v0.13.22 server started at http://localhost:9876/
22 04 2016 15:09:29.857:INFO [launcher]: Starting browser Chrome
22 04 2016 15:09:32.121:INFO [Chromium 49.0.2623 (Ubuntu 0.0.0)]: Connected on socket /#mKEDUObYOHij-U8oAAAA with id 963508
Chromium 49.0.2623 (Ubuntu 0.0.0) Test gl plot interactions gl3d plots scatter3d click events should have FAILED
    TypeError: Cannot convert undefined or null to object
        at Object.<anonymous> (/tmp/875c384a1d041134119e6fd6cbe578ab.browserify:104549:31 <- tests/gl_plot_interact_test.js:141:0)
LOG: 'lost context'
LOG: 'lost context'
LOG: 'lost context'
LOG: 'lost context'
LOG: 'restyle fail', undefined, '', undefined
LOG: 'relayout fail', undefined, false
LOG: 'type newtype already registered'
LOG: 'Oops, tried to put a polar trace on an incompatible graph of cartesian data. Ignoring this dataset.', Object{type: 'newtype', r: 'this is polar'}
Chromium 49.0.2623 (Ubuntu 0.0.0): Executed 773 of 773 (1 FAILED) (1 min 6.717 secs / 1 min 6.225 secs)

[n-riesco]

Using #467 all jasmine tests pass.

[etpinard]

Thanks!