[dive] send information about roots in the graph

headers/header_spec.txt

ivette/api/plugins/dive/index.ts

ivette/src/frama-c/dive/Dive.tsx

ivette/src/frama-c/dive/style.json

src/plugins/dive/Makefile.in

src/plugins/dive/build.ml

src/plugins/dive/build.mli

src/plugins/dive/context.ml

src/plugins/dive/context.mli

src/plugins/dive/dive_graph.ml

src/plugins/dive/dive_graph.mli

src/plugins/dive/dive_types.mli

src/plugins/dive/main.ml

src/plugins/dive/server_interface.ml

src/plugins/dive/tests/dive/oracle/assigned_param.dot

src/plugins/dive/tests/dive/oracle/callstack_global.dot

src/plugins/dive/tests/dive/oracle/callstack_strategy.dot

src/plugins/dive/tests/dive/oracle/const.dot

src/plugins/dive/tests/dive/oracle/exceptional.dot

src/plugins/dive/tests/dive/oracle/global.dot