Calculate coverage and submit to coveralls.io

https://coveralls.io/r/edx/xblock-sdk
Merge pull request #42 from stvstnfrd/coveralls

Calculate coverage and submit to coveralls.io
Add gruntserver command

This is to be used in place of `runserver`. In addition to performing
`runserver`'s tasks, it also launches the `grunt watch` listener.
Un-hard-code Gruntfile location
Order imports alphabetically
Name methods consistently
Factor out list comprehension

It led to repetition of code, as we need to perform multiple tasks on
the data.
Create helper "write" method
Add missing docstrings
Simplify import
Clean up syntax and naming
Un-hard-code "os.path.sep"
Normalize console logging
Fix failing test