Add find_package(SQLite3) required by fhiclcpp

Latest fhiclcpp module requires and exposes SQLite3 interfaces.
Import FindSQLite3 CMake module to locate the library and headers.
Add find_package call in main CMake script, requiring a minimum
version of 3.7.15 due to the use of the sqlite3_errstr function
in fhiclcpp.
Build fhiclcpp module using new subtree structure

Update paths in fhiclcpp_module.cmake to reflect subtree structure.

Move setup of tests for fhiclcpp, cpp0x and cetlib after build of
FNALCore, but before installation. Use of link_directories command
in cetlib and fhiclcpp CMake test scripts causes cyclic dependencies
if used before FNALCore is built.

Ignore tests for fhiclcpp for now by returning directly from the
fhiclcpp_module_tests file when it is included.

Add fhiclcpp OBJECT library and headers paths to build of FNALCore.
Link FNALCore to SQLite3 library, recording it in the PUBLIC
interfaces as fhiclcpp exposes the sqlite3 interface to clients.