Bug 1098254 - Add JSONLint to gruntfile, fix JSLint warnings and add .idea to .gitignore

introduce .idea folder in gitignore for those who edit in jetrains IDEs

enhance grunt usage + use of JSONLint tool to validate JSON files

unused parameters + unneeded comma + filter loop from enumerables inherited properties

enhancements to gruntfile suggested by Alex Gibson

fix code style
Merge pull request #2462 from MathRobin/master

Enhancements to the JS part + enhance gruntfile + ignore Jetbrains IDE config folder