BLX-7 (8.30) Add cvscan support to gda.scripts.scan.trajscans package

This needs to be refactored to move the ContinuousMixin, CvMixin and
CvScan classes into their own packages.
Merge remote branch 'i10-prod/8.30' into 8.30
Merge remote branch 'i10-prod/8.30'
Merge branch '8.30'