update libadb and make other useful changes

@ochameau: this updates the ADB Helper addon to libadb 0.6, the latest version. It also adds a useful .gitignore rule and fixes a Makefile issue that causes the Helper addon to be missing the ADB library when you do `make package` without having previously done `make run` (because the library was only being copied to *helper/data/* on `make run`).