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 seems moot, just use https://github.com/adametry/gulp-eslint#eslintfailonerror