SFTPDocumentsProvider: do not add port to title if canonical

SFTPDocumentsProvider: add summary

SFTPDocumentsProvider: correct connection resetting

SFTPDocumentsProvider: proper error handling

SFTPDocumentsProvider: refactor toasting

reformat code

fix various lints

build: bump sshlib to 2.2.20

seekable reader, bump min sdk level to 26

build: modernize toolchain

README: we support custom path now

don't reuse SFTPv3Client, it's not costy and this enables concurrency

ReadTask: always try to close the file

add mount path settings

show configured values on create

adjust inputType

close connection on query roots

notify root change when config changes

NetworkOnMainThreadException workaround

reuse connection whenever possible