Make Random*Generators be seedable

This is a necessary step to fix issue with combining multiple
random generators in one test case, with different section nesting.

src/CMakeLists.txt

@@ -222,6 +222,7 @@ set(IMPL_SOURCES
     ${SOURCES_DIR}/internal/catch_wildcard_pattern.cpp
     ${SOURCES_DIR}/internal/catch_xmlwriter.cpp
     ${SOURCES_DIR}/internal/catch_test_case_info_hasher.cpp
+    ${SOURCES_DIR}/generators/catch_generators_random.cpp
 )
 set(INTERNAL_FILES ${IMPL_SOURCES} ${INTERNAL_HEADERS})