v1.7.3

Changes

• DataBOX sending update
• Modernize Debian packaging: debhelper-compat 13, remove composer-debian
• Refactor PHP source: extract Upominka::debtAmount(), fix ByDatovka bugs (null-deref, config logic error, curl crash/timeout), fix RemindMailer::addFile() return value, remove dead code
• Debian packaging: InstalledVersions baked in at build time, AppStream metainfo fixed (type console-application, appstreamcli validation), man pages for all installed binaries