Construct paths relative to the Cuberite sources with PROJECT_SOURCE_DIR, instead of wherever the first CMakeLists.txt file happened to be with CMAKE_SOURCE_DIR.
In Android's case, the latter was in a folder called android/ but that's not the root of the source tree, so any file path built off that root was wrong. This caused file-specific warnings exclusions to fail to apply.
Closes#4708
This updates jsoncpp, mbedtls, TCLAP and SQLiteCpp to their latest stable release. A few additional changes were needed:
* jsoncpp deprecated Reader, FastWriter and StyledWriter which I've replaced
with some helper functions in JsonUtils.cpp
* SQLiteCpp changed how it builds with external sqlite libraries, now expecting
them to be installed. The simplest path was to remove sqlite from cuberite's
submodule and just use SQLiteCpp's internal version.
