Add new JSON value assignment feature

This commit adds a new file containing a recursive algorithm which,
given an exprt and a JSON representation of a value for the exprt,
produces codet that assigns the exprt to that value.
Some helper functions in other files are also added.

Author: antlechner

jbmc/src/java_bytecode/Makefile

@@ -1,4 +1,5 @@
-SRC = bytecode_info.cpp \
+SRC = assignments_from_json.cpp \
+      bytecode_info.cpp \
       character_refine_preprocess.cpp \
       ci_lazy_methods.cpp \
       ci_lazy_methods_needed.cpp \