Show warning when using cached database

[jhung0]

When switching between image and object classification (using the same database), you need to delete the old db file (default location in mac is /Users/[name]/CPA/) before loading the properties file otherwise the old db file will be used. There should be a warning about this.

[braymp]

Why not remove the view/tmp table on CPA close?

[braymp]

Also, I'm not sure why this is a problem in the first place. If the image_classification field is not set, doesn't it just revert to the original per-object table specified in the props file?

[jhung0]

We came across a problem when we ran the example properties file and then closed CPA and ran it again adding image_classification = True. The problem was fixed if the old db file was removed.

[braymp]

I think the problem should be dealt with in some way other than blowing away the db; for a large dataset, removing the db constitutes losing a lot of work. Is this sqlite only, or in mysql also?

[jhung0]

I'd suggest copying the database and renaming it and changing the properties file

[jhung0]

Also I haven't had any issue with mysql, just sqlite

[AnneCarpenter]

Is the proposed fix here to just create a warning? Or to actually mess with the database? Seems like the former is more tractable and less controversial.