Prefer LD_LIBRARY_PATH to hardcoded search paths

For server-side and also packaged desktop applications, it is preferable to load a known specific ```libsqlite3.so``` that has the necessary features compiled in, to using whatever ```libsqlite3.so``` the OS happens to supply.

BTW, on Ubuntu 18.04 the system-supplied ```libsqlite3.so``` lives in ```/usr/lib/x86_64-linux-gnu``` which isn't in the current hardcoded paths.

