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.

tests/test_paste.py

@@ -23,7 +23,7 @@ import unittest
 from typing import ClassVar
 from unittest import mock
 
-import paste
+from dikte import paste
 from tests.support import DikteTest, FakeCompleted, only_these_tools