Added extension to display merge prototype on ipython notebook.

Known bugs:
-chrome.png, and firefox.png shows a bug in displaying graphs.
-certain cells are minimized.
-left side of the UI is a bit cut off also observed in html prototype.
Added the .ipynb used to generate merge extension example
JSON spec test cases.
Verify the JSON for specs on travis
Add node_modules/ to .gitignore.
Fixing syntax errors in JSON
Fixing syntax errors in JSON specs
Moving single character test cases to separate file.
Fix missing comma.
Missing comma, superfluous comma
Remove simple tests from test_cases.json
Rename test_cases to test_cases_cells
Fix remaining syntax errors in test_cases_cells.json
Add code to specs example test
Merge branch 'marwa-fixedmoretestcases'
Add new spec files to build.
try to get buttons work
Fix arrow-buttons moving left/right cells into base.
Don't obliterate all notebooks. Only process notebooks with nbdiff metadata.
Add logging statements.