MainMenu: Create MainMenu map

[x] Create new empty level saved as MainMenu
[x] MainMenu contains a main widget blueprint (or similar if does the job, like maybe switcher as example, but don't think so)
[ ] MainMenu has an accessible button to load the first dev test map
[ ] MainMenu has an accessible button to load both basix gym
[ ] can load Frank Gym from main menu
[ ] can load Charles gym from main menu
[x] MainMenu uses its own GameMode BP
[x] MainMenu uses its own default pawn
[x] MainMenu uses its own playercontroller (players creation will be re thinked in each test maps/gamemodes)
[ ] MainMenu has a button to quit the game to desktop
[x] MainMenu has its own HUD, to be used to create needed widgets in a way that the gamemode just create the hud, then the rest should be managed by the HUD (for creation, GameMode should and will be used to manage multiple thing but should call methods from relevant elements)

Dev-Miner / CharlesInTown