18.1.0-alpha.4

92928ad5a [IMP] export: flattent cell object Task: 4295344
782ca4336 [REF] export: remove ExcelCellData Task: 4295344
19b2faa92 [REF] export: remove useless property Task: 4295344
c02873b21 [REF] xlsx: remove some custom values in ExcelCellData Task: 4295344
65ec7d471 [REF] import: helper to denormalized data Task: 4295344
a3dfe6d29 [FIX] chart: date line chart Task: 4268977
3b8935c04 [IMP] charts: allow chart insertion with unbounded zone Task: 3502197
4c80b4776 [IMP] icons : use fa-clipboard icon for copy-to-clipboard buttons Task: 3181092
589eee060 [IMP] charts: enable "Show Values" on radar chart Task: 4282824
7225e7ead [FIX] color_picker: conditionally hide reset button Task: 4102704
0b1ba7f68 [REF] charts: simplify runtime generation Task: 4286137
7bda5f911 [REM] charts: remove useless, wrong and misleading test Task: 4286137
f15003351 [FIX] chart: trend line of area chart Task: 4274294