update libadb and make other useful changes

@ochameau: this updates the ADB Helper addon to libadb 0.7, the latest version. It also adds a useful .gitignore rule, 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`), and breaks the dependency on a remote libadb package even when you're building adb locally. Plus a bit of refactoring.