add configuration to disable parts of the UI

Some users do not like to see parts of the UI. While the diff window will not be
displayed if there is nothing to preview, the details window always pops up. To
allow for better customization, global variables have been added to control the
visibility of each window, except the main menu.

Author: weilbith

README.md

@@ -86,3 +86,18 @@ files yourself and get the full power of customization.
 At the current state of documentation I must redirect you to the syntax files in
 the source code of the plugin to get a list of available highlight groups. The
 user can simply overwrite any of the default mappings to his liking.
+
+### Disable parts of the UI
+
+The following global variables can be set to disable parts of the user
+interface:
+
+```lua
+vim.g.code_action_menu_show_details = false
+vim.g.code_action_menu_show_diff = false
+```
+
+```vim
+let g:code_action_menu_show_details = v:false
+let g:code_action_menu_show_diff = v:false
+```

lua/code_action_menu.lua

@@ -62,35 +62,47 @@ local function open_code_action_menu()
   end
 end
 
-local function update_selected_action()
-  local selected_action = menu_window_instance:get_selected_action()
-
-  if details_window_instance == nil then
-    details_window_instance = DetailsWindow:new(selected_action)
-  else
-    details_window_instance:set_action(selected_action)
+local function update_details_window(selected_action)
+  if
+    vim.g.code_action_menu_show_details == nil
+    or vim.g.code_action_menu_show_details
+  then
+    if details_window_instance == nil then
+      details_window_instance = DetailsWindow:new(selected_action)
+    else
+      details_window_instance:set_action(selected_action)
+    end
+
+    local window_stack = { anchor_window_instance, menu_window_instance }
+
+    details_window_instance:open({ window_stack = window_stack })
   end
+end
 
-  details_window_instance:open({
-    window_stack = {
-      anchor_window_instance,
-      menu_window_instance,
-    },
-  })
+local function update_diff_window(selected_action)
+  if
+    vim.g.code_action_menu_show_diff == nil or vim.g.code_action_menu_show_diff
+  then
+    if diff_window_instance == nil then
+      diff_window_instance = DiffWindow:new(selected_action)
+    else
+      diff_window_instance:set_action(selected_action)
+    end
 
-  if diff_window_instance == nil then
-    diff_window_instance = DiffWindow:new(selected_action)
-  else
-    diff_window_instance:set_action(selected_action)
+    local window_stack = { anchor_window_instance, menu_window_instance }
+
+    if details_window_instance ~= nil then
+      table.insert(window_stack, details_window_instance)
+    end
+
+    diff_window_instance:open({ window_stack = window_stack })
   end
+end
 
-  diff_window_instance:open({
-    window_stack = {
-      anchor_window_instance,
-      menu_window_instance,
-      details_window_instance,
-    },
-  })
+local function update_selected_action()
+  local selected_action = menu_window_instance:get_selected_action()
+  update_details_window(selected_action)
+  update_diff_window(selected_action)
 end
 
 local function execute_selected_action()