* Avoid overriding argv/argc via `CMD_UTILS_CONVERT_ARGS_TO_UTF8` in
Windows-specific code when processing arguments from a 2nd instance
* Move the other startup code to main as well as they are not needed when
processing arguments from a 2nd instance
* Improve debug logging
* Use `waitForBytesWritten()` instead of `flush()` when passing args as
recommended by the documentation
* Avoid use of `bytesAvailable()` as it doesn't work as expected in this
situation on Windows (likely it doesn't really work reliably on all
platforms); calling `readAll()` works and is simpler anyways
* Tested that `--replace` works as well; also the
`waitUntilGone && QFile::exists(fullServerName)` block is entered and if
the previous instance is taking some time it really waits until it is
gone
* Make functions in `main.cpp` static as they are not used by
other units
* Delete the `TrayIcon` via an extra parent object that is
deleted before the `QNetworkAccessManager` is deleted; otherwise
the destruction of `SyncthingConnection` (which aborts pending
replies) might access dangling `QNetworkReply` objects
* Improve error handling in `SingleInstance` code
* Allow to replace the current instance via the new `--replace`
argument; this may be useful when creating an installer/updater
Create a distinct server for each user so they don't interfere with each
other. Otherwise the instance of the second user tries to connect to the
instance started by the first user which fails and therefore breaks the
single instance behavior for the second user.
Martchus