More logging of potentially slow operations

[abyrd]

The first time you do an analysis via the analyst web UI, it reports "processing query" for a long time. Even when all components are running locally, there is no sign from any component that any long-running operation is in progress, or even that it has started. This leaves you wondering if it's actually doing anything or just stalled. We should log the beginning and end of any potentially slow one-off operation. This is especially necessary when testing locally because there is a lot of data transfer to and from Amazon S3. On an ADSL connection this can be extremely slow (uploading 100MB PBF files at 250kB/sec). It helps to at least have some indication of what's happening or the whole system feels broken.

Equivalent issue on R5 repository: conveyal/r5#18