Add configuration for vim

- Add ~/.config/vim/vimrc
  + Configure basic stuff
  + Activate spell checks
  + Activate syntax highlighting and ruler
  + Show whitespace characters
  + Add various snippets for mouse handling,
    toggling line numbers, and search
  + Set `vim`-related directories inside
   ~/.config/vim and ~/.local/state/vim
- Integrate extra settings for Python files
  in ~/.config/vim/after/ftplugin/python.vim
- Add `vim` artifacts in ~/.config/git/ignore

.inputrc

@@ -0,0 +1,14 @@
+# Enable vi-style line editing for all readline apps
+set editing-mode vi
+
+# Indicate the current mode via the cursor shape
+set show-mode-in-prompt on
+set vi-cmd-mode-string "\1\e[2 q\2"  # steady block
+set vi-ins-mode-string "\1\e[5 q\2"  # blinking beam
+
+# Ctrl-L clears the screen in command mode only
+# => Bind in insert mode as well
+set keymap vi-insert
+"\C-l": clear-screen
+
+set keymap vi