Explicitly check for the tokenizer source file to check that
the name is correct. We can't use the import error for that
because it hides other import errors like a missing
library.
Fixes#2327.
This adds an installation step for PHP code for the tokenizer. The
PHP code is split in two parts. The updateable code is found in
lib-php. The tokenizer installs an additional script in the
project directory which then includes the code from lib-php and
defines all settings that are static to the database. The website
code then always includes the PHP from the project directory.
Adds a migration that initialises a legacy tokenizer for
an existing database. The migration is not active yet as
it will need completion when more functionality is added
to the legacy tokenizer.
This adds the boilerplate for selecting configurable tokenizers.
A tokenizer can be chosen at import time and will then install
itself such that it is fixed for the given database import even
when the software itself is updated.
The legacy tokenizer implements Nominatim's traditional algorithms.
