#12 libodfgen: getAddressString: support list of addresses

[ryanjmulder]

Attributes like table:cell-range-address, chart:label-cell-address, chart:values-cell-range-address, etc. all have type cellRangeAddressList, which is "a list of cell range addresses and cell addresses. Each item in the list is separated by white space."

This patch updates OdcGeneratorPrivate::getAddressString to convert a vector with multiple elements into a string with space-separated addresses. (getAddressString previously limited the vector to having a single element)

[alonso laurent]

Hello, thank for the patch, I add it in https://sourceforge.net/p/libwpd/libodfgen/ci/4645e484c88ae5450ba7ee7ddaa69a71ba65b6cd/