InsertRow / DeleteRow / InsertColumn / DeleteColum do not update formulas on other sheets

[JanKallman]

To reproduce:

        [TestMethod]
        public void DeleteIssue()
        {
            using (var p = new ExcelPackage())
            {
                var ws1 = p.Workbook.Worksheets.Add("Sheet1");
                var ws2 = p.Workbook.Worksheets.Add("Sheet2");
                ws1.Cells["A10"].Value = 1;
                ws1.Cells["A11"].Formula = "A10*2";
                ws1.Cells["A12"].Value = 3;
                ws2.Cells["A1"].Formula = "SUM(Sheet1!A10:A12)";
                ws1.DeleteRow(1);
                Assert.AreEqual("A9*2",ws1.Cells["A10"].Formula);
                Assert.AreEqual("SUM(Sheet1!A9:A11)",ws2.Cells["A1"].Formula);
            }
        }

[JanKallman]

EPPlus did not update formula references for cross-sheet addresses. This commit updates the behavior methods InsertRow / DeleteRow / InsertColumn / DeleteColum.
DeleteRow and DeleteColumn will now set deleted cells in a formula to #REF! if fully deleted or shrink the addresses if partial deleted.

[JanKallman]

EPPlus RC