ui: import and export .pqw files from the menus

The basic interface gets two main menu entries that ask for a path.
The curses roster gets [I] Import and [E] Export, with a new text input
view for the path, prefilled with NAME.pqw on export, and a message
view for the outcome and any warnings. The README explains how to move
characters to and from the web version.

Resolves #21

pqcli/ui/curses/views/__init__.py

@@ -8,7 +8,9 @@ from .create_character_view import (
     ChooseCharacterStatsView,
 )
 from .game_view import GameView
+from .message_view import MessageView
 from .roster_view import RosterView
+from .text_input_view import TextInputView
 
 __all__ = [
     "BaseView",
@@ -19,5 +21,7 @@ __all__ = [
     "ChooseCharacterRaceView",
     "ChooseCharacterStatsView",
     "GameView",
+    "MessageView",
     "RosterView",
+    "TextInputView",
 ]