Merge branch 'new-index-space-structure-v2' into 1.6

extra/schema_fill.lua

src/box/alter.cc

src/box/bootstrap.snap

src/box/key_def.cc

src/box/key_def.h

src/box/lua/index.cc

src/box/lua/schema.lua

src/box/lua/space.cc

src/box/memtx_bitset.cc

src/box/memtx_engine.cc

src/box/memtx_hash.cc

src/box/memtx_rtree.cc

src/box/memtx_tree.cc

src/box/schema.cc

src/box/sophia_engine.cc

src/box/sophia_index.cc

src/box/space.h

src/box/sysview_index.cc

src/lua/net_box.lua

test/box/access_misc.result