Graph: cleanup from audit
Graph: improve recurrence handling, firstDayOfWeek is required for weekly patterns in Graph
Graph: implement full folder caching on top of delta sync, based on ConcurrentHashMap and ReentrantLock
Graph: set both size limit ($top) and max page size (odata.maxpagesize) in searchMessages, log item count in fetchNextPage
Graph: initial implementation of folder delta sync support, enable with davmail.graph.deltaSync=true
Graph: introduce refreshMessages to prepare delta sync
Graph: unit test for delta sync
Graph: cleanup from audit