fix compilation error in core_io.h

- error: 'vector' in namespace 'std' does not name a type
- add <vector> include in core_io.h
- remove <vector> includes from core_read.cpp and core_write.cpp
add license header to core_io.h, core_read/_write.cpp
Restored functionality where the network a Bitcoin URI address applies to is used to determine
the network the client uses, altered such that invalid addresses do not incorrectly send the
user to the test network.