Bug 442157 LinkLF : labels support

- Custom offset convention to avoid moving the link-end's labels after
any manipulation with the link's bendpoints
- Custom label locator's to enforce the new convention

Change-Id: Ia201a1f8021da247acbee3bd184bf02e4e284c5c
Signed-off-by: mgolubev <golubev@montages.com>
4 files changed