dev(Code Coverage): Add Tooling for the Code Coverage
dev(Code Coverage): Add Tooling for the Code Coverage

 - Added Code Coverage dev dependencies
 - Added Code Coverage npm command:
   > coverage to run tests and aggregate coverage stats from it, as well as
   generating an html report out of it.
 - Set fixed version dependencies for istanbul and istanbul-api:

    Due to a packaging mistake on istanbul-api, the current istanbul 1.0.0-alpha
    packages' dependencies are currently broken. Indeed, some packages are named
    1.0.0-aplha.? instead of 1.0.0-alpha.?; which means that npm interprets the
    mistakenly named releases 1.0.0-aplha.? as being higher version that the more
    recent alpha releases.

    One way to fix this is to rely on installing a specific version instead of
    relying on the string comparison to find the highest version of the package.

scality/S3,scality/S3,scality/S3,truststamp/S3,truststamp/S3,tomateos/S3,scality/S3,tomateos/S3,tomateos/S3,scality/S3,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote,tomateos/S3,lucisilv/Silviu_S3-Antidote,truststamp/S3,lucisilv/Silviu_S3-Antidote,truststamp/S3,lucisilv/Silviu_S3-Antidote,tomateos/S3,scality/S3,truststamp/S3,truststamp/S3,lucisilv/Silviu_S3-Antidote,truststamp/S3,tomateos/S3,truststamp/S3,tomateos/S3,tomateos/S3,scality/S3,scality/S3,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote