Add SQLite option to scraper and aggregator

[ccwoolfolk]

When processing a large number of files, it may be more efficient to write to a simple sqlite table instead of creating a json file for every dicom file. For example:

attribute	value
"0010,0020"	"patient-id-12345"
"0010,0040"	"M"
...	...
"0010,0040"	"O"

This functionality can be used by passing an attribute to the script. E.g., python scraper.py --use-sqlite "sqlite-db-file-name".