AST-1607 Fix startchan support in MSReader and Filter; Set version to 6.2.0
- Add tests for msin.startchan, with and without filter.startchan.
- Update the correct channel(s) when using msin.startchan.
- Update DPInfo::start_channel_ correctly when it already is non-zero.
- Split DPInfo::update into SelectChannels and SelectBaselines.
- Remove start_channel from DPInfo constructor, since it's 0 in all calls. SelectChannels should be used instead now.
Edited by Maik Nijhuis