Made project accessible in the filter and relocation context

Sometimes I need to work with the project property when I specify filters or relocations.

```
shadow {
    relocation {
        pattern = 'com.example.test'
        shadedPattern = 'com.example.test.v' + project.test_Version
    }
}
```

This doesn't work because of the following error:
```
> No such property: project for class: com.github.jengelman.gradle.plugins.shadow.impl.ArchiveRelocation
```