blockdiagram: make all composition fields optional
move cppdemo to blockdiagram representation
mqueue: finished implementation
blockdiagram: allows connections to/from iblocks, resolve ptrs
doc update
core,types: store seqid in ubx_node_ref_t.

This makes the seqid node specific, and avoids errors caused by
loading types into Lua.

This also allows to run the unit tests in one process with multiple
nodes. Also fix the broken tests/test_struct_comm.lua test.