ENH: Update DICOM Database with URL Support and Tag Cache Optimization

This generalizes the ctkDICOMDatabase code to ease hard-coded restrictions about
DICOM files always being on disk. Now the schema includes a `URL` field of the
SQLite database so certain file-specific operations are only performed on filePaths
while URL are handled independently. Entries in the `Images` table of the database
may now have either a `URL` or a `fileName` or both and new accessors are provided
to get `URL`s at the series and instance level.

Schema version is updated from version `0.7.0` to `0.8.0`.

Also this contains a fix to the `ctkDICOMTagCache` so that tags are always stored
internally as uppercase hex, so a string like "0010,000d" will always be turned
into "0010,000D" for storage in the database. Both forms can be used to query
tags. This avoids the situation where some cache entries were duplicated because
different code used either upper or lower case to refer to the same tag. Using
only upper case should improve storage use and improve performance by avoiding
unneeded cache misses.

Co-authored-by: Andras Lasso <lasso@queensu.ca>
Co-authored-by: Davide Punzo <punzodavide@hotmail.it> 
Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

Libs/DICOM/Core/Resources/dicom-schema.sql

@@ -23,11 +23,12 @@ DROP INDEX IF EXISTS 'SeriesStudyIndex' ;
 DROP INDEX IF EXISTS 'StudiesPatientIndex' ;
 
 CREATE TABLE 'SchemaInfo' ( 'Version' VARCHAR(1024) NOT NULL );
-INSERT INTO 'SchemaInfo' VALUES('0.7.0');
+INSERT INTO 'SchemaInfo' VALUES('0.8.0');
 
 CREATE TABLE 'Images' (
   'SOPInstanceUID' VARCHAR(64) NOT NULL,
-  'Filename' VARCHAR(1024) NOT NULL ,
+  'Filename' VARCHAR(1024) NULL,
+  'URL' VARCHAR(2048) NULL,
   'SeriesInstanceUID' VARCHAR(64) NOT NULL ,
   'InsertTimestamp' VARCHAR(20) NOT NULL ,
   'DisplayedFieldsUpdatedTimestamp' DATETIME NULL ,
@@ -84,7 +85,8 @@ CREATE TABLE 'Series' (
   'DisplayedFieldsUpdatedTimestamp' DATETIME NULL ,
   PRIMARY KEY ('SeriesInstanceUID') );
 
-CREATE UNIQUE INDEX IF NOT EXISTS 'ImagesFilenameIndex' ON 'Images' ('Filename');
+CREATE INDEX IF NOT EXISTS 'ImagesFilenameIndex' ON 'Images' ('Filename');
+CREATE INDEX IF NOT EXISTS 'ImagesFilenameIndex' ON 'Images' ('URL');
 CREATE INDEX IF NOT EXISTS 'ImagesSeriesIndex' ON 'Images' ('SeriesInstanceUID');
 CREATE INDEX IF NOT EXISTS 'SeriesStudyIndex' ON 'Series' ('StudyInstanceUID');
 CREATE INDEX IF NOT EXISTS 'StudiesPatientIndex' ON 'Studies' ('PatientsUID');