Add script to manually import annotations from analyst CSVs (#487)

This adds a script that will read a CSV matching the format of our analysts’ current sheets and create annotations in the database for each row. Run it like:

    scripts/annotations_import <PATH_TO_CSV>

Add the `--is_important_changes` option if the sheet represents “important” changes. This mainly affects how the `significance` field is calculated.

This is a component of edgi-govdata-archiving/web-monitoring#141

.env.example

@@ -40,4 +40,4 @@ export ACCESS_CONTROL_ALLOW_ORIGIN_HEADER="*"
 
 # Uncomment to enable logging. Set the level as any normal level.
 # https://docs.python.org/3.6/library/logging.html#logging-levels
-# LOG_LEVEL=INFO
+# export LOG_LEVEL=INFO