Blender Git Loki

LibOverride: Add own flag to copy or not overrides to ID copy code.

Relying on only no-main for that was weak, and inn the end it turns out
we sometimes also need to ifnore override data during copy of Main
data-blocks.

NOTE: The new `LIB_ID_COPY_NO_LIB_OVERRIDE` is also added to the
`LIB_ID_COPY_LOCALIZE` set of flags.

NOTE: The fact that we may now copy liboverrides in some non-main cases
may cause issues in some cases, pretty impossible to track all possible
ones from reading the code... Would not expect too many problem though,
usages of `LIB_ID_CREATE_NO_MAIN` by itself are not so common.