/*
Add value to storage
- key: key to retrieve data
- value: value of data
- keep: *optional* boolean to keep value indefinitly (localStorage) or temporarily (sessionStorage)
function (key, value, keep) {

            // Get storage type
            keep = (typeof keep === 'undefined' || typeof keep !== 'boolean') ? false : keep;
            var storageType = keep ? 'localStorage' : 'sessionStorage';

            // Convert undefined values to null
            if (angular.isUndefined(value)) {
                value = null;
            } else if (angular.isObject(value) || angular.isArray(value)) {
                value = angular.toJson(value);
            }

            // Set web storage
            webStorage = $window[storageType];

            // Add data to storage
            webStorage.setItem(key, value);

            return true;
        }