feat(Core/Battlegrounds): Enhanced bg system for modules

[Helias]

This PR allow to:

• add other BGs as module that need to exchange data for "capture flags" or "assault base" and so on.

CHANGES PROPOSED:

• restored old switch case related to 75bf44d
• added hashmaps and conditions before several switch case

TESTS PERFORMED:

• joined Warsong Gulch, Arathi Basin and played them until the end
• joined different battlegrounds using Random Battleground

OS: Linux - Ubuntu 18.04.3 LTS

HOW TO TEST THE CHANGES:

• join battlegrounds and finish it (capture the flag on Warsong Gulch, assault base on Arathi Basin etc.)
• join also using random battleground
• join some arenas and finish it

[Helias]

Still need to check different things, it is not ready.

[Helias]

To be honest, I don't really like the solution refactoring switch case into hashmaps, in these days I thinked about it and I find a solution.
It consists into adding hashmaps empty and if a module fill them the core will check and eventually use them, otherwise, it continue to use the switch case.

Indeed, I restored also the old switch case code (related to 75bf44d) to mantain the core TC-like ;-)

I tested this PR using two different mod-bg-*, to test this PR are not necessary the modules just test the normal battleground and arenas.

[Helias]

This is now a duplicate of #2521
Hence, I'm closing it and deleting the branch, anyway test the new PR of Shard asap pls!