Previously, `makeLogHandler()` hardcoded "standard" as the logfile name
passed to `getLogWriter()`, causing all log categories (`database`,
`http`, `events`, `mail`) to write to `standard.log` instead of their
own files.
Add a logfile parameter to `makeLogHandler()` so each caller specifies
its category name, producing `database.log`, `http.log`, `echo.log`,
`events.log`, and `mail.log` as expected.
Fixes https://github.com/go-vikunja/vikunja/issues/2177