Calculate ‘filesize’ column from the journal entry data

As a fallback. If the metadata contains a different filesize, that’s
used in preference.
Add a Vim-style modeline to the file

So I don’t keep entering tabs by mistake.
Minor code refactoring and cleanups
Add a ‘hostname’ column to the URIs CSV file

This allows statistics to be gathered based on the hostnames accessed
when browsing the web, which is probably more useful than the precise
pages.