The default encoding for source files is UTF-8 since Python 3, so we can
drop all encoding headers. While we are at it, just replace them with
SPDX headers.
This is a first step for #42. Since most access to the scraper classes
is through instances, modules can now dynamically override url and name
(name is now a property).
Maintaining the descriptions creates quite a bit of overhead (finding
them, copying them, checking if they are still correct) for a minimal
user benefit.
PS: Viewing this diff should be easier in a difftool that shows changes
in a line, for example kdiff3.
