Merge master: the modules moved into a package

Every file this branch touches moved into dikte/, so the merge is mostly the
rename following the edits. What needed a hand:

hotkey.py: master replaced the _macos()/_gnome() pair with one backend()
chooser, and this branch had added _windows() to the pair. Windows is a fifth
value of the chooser now, and everything that used to ask "macOS or Windows?"
asks backend() instead. The key is held by the running process there, so
installs_shortcuts() and shortcut_needs_restart() are both false for it, and
desktop_name() says Windows.

install.ps1 and the Windows README name dikte/__main__.py, the entry point the
Linux and macOS installers were pointed at in the same commit. The Start Menu
entry, the autostart entry and the dikte.cmd shim all come off one $entry
variable.

settings_ui.py: the shortcut tab now has a Windows sentence of its own, with
the Turkish for it. Falling through to the branch master wrote for a desktop
with no registry would have told a Windows user to check /dev/input. Nothing
covers that branch: there is no Windows Settings test class, the way there is
one for macOS.

CONTRIBUTING: the chooser it names is backend() now, and the test count is the
merged one, 1067 of 1110 running anywhere.

install.ps1

@@ -11,6 +11,9 @@ param(
 
 $ErrorActionPreference = "Stop"
 $repo = $PSScriptRoot
+# The one file that starts the application, whoever is asking: the Start Menu
+# entry, the autostart entry and the dikte command all name it.
+$entry = Join-Path $repo "dikte\__main__.py"
 $startMenu = [Environment]::GetFolderPath("Programs")
 $startup = [Environment]::GetFolderPath("Startup")
 $shortcut = Join-Path $startMenu "Dikte.lnk"
@@ -55,7 +58,7 @@ $shell = New-Object -ComObject WScript.Shell
 foreach ($path in @($shortcut) + $(if ($Autostart) { @($autostartLink) } else { @() })) {
     $link = $shell.CreateShortcut($path)
     $link.TargetPath = $pythonw
-    $link.Arguments = "`"$repo\dikte.py`" --gui"
+    $link.Arguments = "`"$entry`" --gui"
     $link.WorkingDirectory = $repo
     $link.Description = "Dikte: dictation"
     $link.Save()
@@ -67,11 +70,11 @@ foreach ($path in @($shortcut) + $(if ($Autostart) { @($autostartLink) } else {
 # the one the command line should run, whatever a later PATH change puts first.
 $shimDir = Split-Path $cmdShim
 if (Test-Path $shimDir) {
-    "@echo off`r`n`"$($python.Source)`" `"$repo\dikte.py`" %*" |
+    "@echo off`r`n`"$($python.Source)`" `"$entry`" %*" |
         Out-File $cmdShim -Encoding ascii
     Write-Host "command: dikte  ($cmdShim)"
 } else {
-    Write-Warning "No $shimDir on this machine, so there is no dikte command. Run it as: python `"$repo\dikte.py`""
+    Write-Warning "No $shimDir on this machine, so there is no dikte command. Run it as: python `"$entry`""
 }
 
 Write-Host ""