Resolve "Login screen setup (without backend)"

Closes #19 (closed)

frontend/assets/menu-textures.atlas

+
+menu-textures.png
+size: 512, 512
+format: RGBA8888
+filter: Nearest, Nearest
+repeat: none
+main-menu-welcome-box
+  rotate: false
+  xy: 228, 438
+  size: 224, 64
+  orig: 224, 64
+  offset: 0, 0
+  index: -1
+menu-background
+  rotate: false
+  xy: 2, 2
+  size: 224, 500
+  orig: 224, 500
+  offset: 0, 0
+  index: -1
+menu-button-rounded
+  rotate: false
+  xy: 228, 392
+  size: 200, 44
+  orig: 200, 44
+  offset: 0, 0
+  index: -1
+tankwars-logo
+  rotate: false
+  xy: 228, 350
+  size: 134, 40
+  orig: 134, 40
+  offset: 0, 0
+  index: -1