Adds difference image

[Cyberboss]

Closes #73

Here is SQL Server migrations for the change

USE MapDiffBotv3;
set xact_abort on;
BEGIN TRANSACTION;

CREATE TABLE Images (ID BIGINT NOT NULL IDENTITY(1,1) PRIMARY KEY, [Data] varbinary(max) NOT NULL, TempInstallalationId BIGINT ,
TempCheckRunId BIGINT, TempFileId int);

ALTER TABLE MapDiffs ADD BeforeImageId BIGINT FOREIGN KEY REFERENCES Images(Id);
ALTER TABLE MapDiffs ADD AfterImageId BIGINT FOREIGN KEY REFERENCES Images(Id);
ALTER TABLE MapDiffs ADD DifferenceImageId BIGINT FOREIGN KEY REFERENCES Images(Id)

INSERT INTO Images ([Data], TempInstallalationId, TempCheckRunId, TempFileId)
 SELECT BeforeImage, InstallationRepositoryId, CheckRunId, FileId FROM MapDiffs AS MD WHERE MD.BeforeImage IS NOT NULL;

UPDATE MD SET BeforeImageId = I.Id FROM MapDiffs MD JOIN Images I 
ON MD.InstallationRepositoryId = I.TempInstallalationId AND MD.CheckRunId = I.TempCheckRunId AND
MD.FileId = I.TempFileId;

ALTER TABLE Images DROP COLUMN TempInstallalationId, TempCheckRunId, TempFileId;
ALTER TABLE Images ADD TempInstallalationId BIGINT, TempCheckRunId BIGINT, TempFileId int;

INSERT INTO Images ([Data], TempInstallalationId, TempCheckRunId, TempFileId)
 SELECT AfterImage, InstallationRepositoryId, CheckRunId, FileId FROM MapDiffs AS MD WHERE MD.AfterImage IS NOT NULL;

 UPDATE MD SET AfterImageId = I.Id FROM MapDiffs MD JOIN Images I 
ON MD.InstallationRepositoryId = I.TempInstallalationId AND MD.CheckRunId = I.TempCheckRunId AND
MD.FileId = I.TempFileId;

 ALTER TABLE Images DROP COLUMN TempInstallalationId, TempCheckRunId, TempFileId;
 ALTER TABLE MapDiffs DROP COLUMN BeforeImage, AfterImage;

COMMIT;