Allow versioning and easy updating of database scheme

[nolden]

Database version should be checked on startup:

• create a const member in ctkDICOMDatabase for the version number of the schema
• create a config table in the database containing a version number
• on instantiaton compare the versions and signal any incompatibility to the application to (optionally) let the user rebuild

The rebuld method:

• select all filenames
• create a second database file with the new schema
• reindex all files and insert to new database
• on success replace old database file

[pieper]

We can document this process and specify that the 'Filename' column of the Images table can never be changed in any future version of the schema (also the version config table schema cannot be changed). This will mean that the database can always be rebuild from the information available in the old database.

[nolden]

Sounds good. I'm already working on the rebuild part. First results will be available soon in the 200-database-schema-update branch.

[nolden]

@pieper Ok, the branch contains now the new updateSchema method that should re-insert everything after applying the schema. The testing is still very basic, see ctkDICOMDatabaseTest2.cpp

[pieper]

We needed this for the SlicerRt project (for a deadline next week) so I finished some of the integration and committed the changes from Marco's branch.

The ctkDICOMAppWidget will auto-update if it sees a version mismatch and provides a dialog. Ideally this should be done with the QFuture pattern to make the progress dialog interruptible, but since this schema update probably happens rarely I didn't add that feature.