Add epoch info for unassociated DA channels

[t-b]

[t-b]

Test "UnassociatedChannelsAndTTLs" uses unassociated DA/AD channels.

• Add write support in EP_CollectEpochInfo
• Allow query support in EP_FetchEpochs
• Visualize it in BSP_AddTracesForEpochs/BSP_EpochGraphToolTip. See also GetLastSettingChannel
• Check NWB writing in NWB_AppendSweepLowLevel, loops at the bottom over unassociated channels. Associated channels already call EP_FetchEpochs/WriteSingleChannel
• Adapt TestNwbExportv2 to also check epochs of unassociated channels
• Check that SF_OperationEpochs works