create a data class for repositories
create a data class for combined revisions
make DBRepositoryInfo implement Comparable
add a field for repository id
change DBCommitInfo to fit the new scheme
create a data class for combined commits
change DBFileInfo to fit the new scheme
change DBFileInfo to fit the new scheme
change DBFileInfo to fit the new scheme
change DBCodeFragment to fit the new scheme
change the scheme of clone set table
change DBCloneSetInfo to fit the new scheme
change DBElementLinkInfo to fit the new scheme
change the sheme of db
change DBCodeFragmentLinkInfo to fit the new scheme
change DBCloneSetLinkInfo to fit the new scheme
change DBCloneGenealogyInfo to fit the new scheme
change DBCloneGenealogyInfo to fit the new scheme
change DBCodeFragmentLinkInfo to fit the new scheme