Feature/allow duplicate bundles in container

[pnoltes]

This PR improves the handling of adding bundles to celix containers, so that:

• If a bundle is added multiple times for the same run level (or for install), the bundle add is ignored
• If a bundle is added, but already exist in another run level (or for install) a warning is printed (but the bundle is still added).

This PR also introduces a WarningTest.cmake in the cmake dir and a ENABLE_CMAKE_WARNING_TESTS option. This option is enabled for conan builds to ensure the warning tests are tested on each platform.

[pnoltes]

LGTM

For embedde bundles, will compiler/linker complain for duplicated bundles? If so, why we allow duplicated bundles for the normal case?

Added check for embedded bundles.