Repackaging: rename scan to labelscan, move direct store access into its own package.

o Scanning for consistency checking was mistakenly confused with label scanning.
Reorganise access to all entries of the label scan store.

o Avoid instanceof checks for checking whether the LabelScanStore supports this feature;
  all implementations now support it.
Update progress monitor while checking label scan store.

o Extract checking code from LabelScanStoreCheckTask to make testing simpler.
Merge pull request #1400 from apcj/2.0-ccheck-cleanup

2.0 ccheck cleanup