Add group info to GroupSummary renderer

[SergeyMaltsev]

Forum post

       /**
         * Renderer function for a single time axis tick in a group summary row.
         * Should calculate a sum and return a html result
         * @param {Date} startDate Tick start date
         * @param {Date} endDate Tick end date
         * @param {Scheduler.model.EventModel[]} events Events which belong to the group
         * @param {Scheduler.model.ResourceModel[]} resources Resources which belong to the group
         * @param {Scheduler.data.EventStore} eventStore Event store
         * @param {Scheduler.data.ResourceStore} resourceStore Resource store
         * @param {Core.data.Model} groupRecord Current groups header row record
         * @param {String} groupField Current groups field name
         * @param {String} groupValue Current groups value
         * @returns {String} Html content
         * @config {Function}
         */