this allows for configuration of the textgrid host from the environment

refactor(config): wrap all settings that can be configured from the environment in an AppConfig object

feat(textgrid_named_dav_provider.py): dav provider which shows titles from metadata in filenames and paths

fix(wsgidav): update wsgidav to 4.0.1; remove requests, zeep; rename config key that has changed with the update

refactor TextgridProject, TextgridAggregation accordingly

close #20

feat(textgrid_dav_provider): provide streamed write to resources with FileLikeQueue and threaded worker

uses a modified version of FileLikeQueue; also, prepare for wsgidav 4 compatibility

provide iterator api and a `__len__` method; read and write according to the length of the incoming stream

uses a `FileLikeQueue` of chunks to streamed directly to the target

also, lint some

close #6

also, default wsgi config "host" to "localhost" and "port" to "8080" if unset; remove "simple_dc" config

allow authentication with username only; deliver a RootCollection built from textgrid projects

a `TextgridConfig` class that reads its values from os env; a `EnvNotSetError` that can be raised on config errors; a `TextgridAuth` class that speaks to the textgrid authentication service