Settings menu: display settings, language codes, style guide window

Display tab: window mode (windowed/maximized/borderless/exclusive), monitor, window
size per monitor (centred, disabled in fullscreen), V-Sync, frame rate cap, reset;
applied and saved at once through the core DisplaySettingsService. Language is read
through LanguageCode (en-en/en_US = English). The window follows the style guide
shell: title and tabs in the header, close on the right, footer hint and per-tab reset.
The main menu hides every session panel of UiHost (pause menu stayed above it).
New suite display_settings (+ --shots); collection_edit leaves the game through the
pause menu and checks it is closed.

test_suites/display_settings/manifest.json

@@ -0,0 +1,10 @@
+{
+  "name": "Display Settings Test",
+  "description": "Integration test of the Display tab of the settings menu: window mode, window size centred on the monitor, borderless fullscreen, frame rate cap, V-Sync, the restore of the saved file on start and the reset; the player's settings file is restored at the end. Activated only by --itest=display_settings (with --frontend, windowed).",
+  "sources": [
+    "src/*.cs"
+  ],
+  "depends": [
+    "menu_base>=1"
+  ]
+}