The name json.hpp conflicts with the JSON for Modern C++ library that
is also used by Developer. Renames json.hpp and json.cpp to jsonpp.hpp
and jsonpp.cpp aka "JSON Pretty Printer".
This change adds integration/regression tests for ibus-keyman. It
re-uses the unit tests that we have for core.
Also modifies one test so that the context doesn't use characters
used in the keyboard. This makes it easier to setup in ibus-keyman
tests.