Put the modules in a package and the scripts in a folder

Twenty-two files at the top of the tree was the first thing anybody saw of
this repository. They are one package now, imported relatively, and the three
scripts that are not the front door moved under scripts/. install.sh stays
where the README has always said it is.

What starts the application is dikte/__main__.py: python3 -m dikte runs it,
and so does naming the file, which is what the launcher symlink, both .desktop
files, the macOS bundle and every registered shortcut do. Run by path there is
no package around it, so it puts the checkout on sys.path itself.

The installers now keep the keys you chose when they are given none, which is
what an update is: update.sh no longer has to read them out and pass them back.
An updater from before this commit cannot read them at all, so the one thing it
can say, the default key with an empty discard key, is read as "nothing was
asked for" rather than obeyed. That guard can go once nobody is updating across
this commit.

tests/test_ui.py

@@ -16,12 +16,12 @@ from PyQt6.QtCore import QPoint, QPointF, Qt
 from PyQt6.QtGui import QWheelEvent
 from PyQt6.QtWidgets import QApplication, QMessageBox
 
-import cleanup
-import config as cfg
-import hotkey
-import overlay as overlay_module
-import paste
-import settings_ui
+from dikte import cleanup
+from dikte import config as cfg
+from dikte import hotkey
+from dikte import overlay as overlay_module
+from dikte import paste
+from dikte import settings_ui
 from tests.support import DikteTest, only_these_tools
 
 # One application for the whole run; Qt allows no second one.
@@ -281,7 +281,7 @@ class Settings(DikteTest):
         text = self.shortcut_tab_text(window)
         self.assertIn("i3 keeps no shortcut registry", text)
         self.assertNotIn("KWin", text)
-        self.assertIn("dikte.py toggle", text)
+        self.assertIn("__main__.py toggle", text)
         # Not a choice to offer where it is the only mechanism there is.
         self.assertTrue(window.evdev_enabled.isHidden())
         self.assertFalse([button for button in
@@ -458,7 +458,7 @@ class MacSettings(Settings):
         text = self.shortcut_tab_text(window)
         self.assertIn("Dikte asks macOS for these combinations", text)
         self.assertNotIn("KWin", text)
-        self.assertNotIn("dikte.py toggle", text)
+        self.assertNotIn("__main__.py toggle", text)
 
     def test_the_paste_keys_on_offer_are_the_ones_a_mac_uses(self):
         window = self.window(cfg.Config())
@@ -482,7 +482,7 @@ class KdeSettings(Settings):
         self.assertIn("KWin only reads shortcut settings at startup", text)
         self.assertIn("Install as a KDE shortcut", text)
         self.assertNotIn("keeps no shortcut registry", text)
-        self.assertNotIn("dikte.py toggle", text)
+        self.assertNotIn("__main__.py toggle", text)
         # Here it is a choice: the wait for the next login, or the key press
         # reaching the focused application as well.
         self.assertFalse(window.evdev_enabled.isHidden())