Add separate weapon variables menu

[MoonPadUSer]

See issue #90
This new menu is supposed to make it easier for newbies and oldies to modify weapons to their desire,
the file I started with was from @IceflowRE but is largely modified by me
This is a first prototype and I'd like to merge it so I can get feedback from the users.

You can show the menu by pressing F7

outdated

[shacknetisp]

Some warnings to fix:

/home/user/src/blue-nebula/src/game/client.cpp: In function ‘void client::writegamevars(const char*, bool, bool, const char*)’:
/home/user/src/blue-nebula/src/game/client.cpp:260:45: warning: comparison with string literal results in unspecified behavior [-Waddress]
         bool export_weapon = weapon_name != "";
                                             ^~
/home/user/src/blue-nebula/src/game/client.cpp:267:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (size_t i = 0; i < ids.size(); i++)
                            ~~^~~~~~~~~~~~

[MoonPadUSer]

on my way...
Edit: Fixed.

[TheAssassin]

In the sense of #100, we should consider adding -Werror -Waddress (and maybe -Wsign-compare) to prevent such issues in the future in a separate PR.