Fix #388: Move admin handler to 'console' module

src/CMakeLists.txt

src/admin.cc

src/admin.h

src/box/box.cc

src/box/lua/load_cfg.lua

src/iproto.cc

src/lua/console.lua

src/lua/init.cc

src/lua/session.cc

src/session.cc

src/session.h

test/app/cfg.result

test/app/console.result

test/app/console.test.lua

test/big/big.lua

test/box/admin.result

test/box/admin.test.lua

test/box/box.lua

test/box/cfg.result

test/box/fiber.result