grunt: initial support of JSHint

* Uses JSHint to lint JavaScript under modules.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
grunt: refactor of Grunt

* Adds copy task for external libraries.

* Removes redundant tasks.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
general: update of README.rst

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>