Add eslint support

Here is an attempt to support `eslint`.
The file `.eslintrc` defines the rules. Usually the value are :
* 0 : do not check
* 1 : warn
* 2 : fail

I have integrated the eslint check in the gulp `static` task.
I have fixed a few files to comply with eslint warnings or errors.

Let me know if you find it usefull

Avi

this is needed because you want to format all the errors, and then fail. When using failonerror it will fail at the first error, not giving you a clear picture of everything that needs to be fix for eslint to pass.