Make use of composed modules

This pull request makes use of the composed modules idea from xp-framework/xp-framework#231 and changes the compiler's test suite to be an extended module inside the `xp-framework/compiler` module.

Before
--
```
Module<xp-framework/compiler:1.9.0-dev>@{
  ** @FileSystemCL<...\xp.thekid.lang\compiler\src\main\php\>
}
Module<xp-framework/compiler.test:1.9.0-dev>@{
  ** @FileSystemCL<...\xp.thekid.lang\compiler\src\test\php\>
}
```

After
--
```
Module<xp-framework/compiler:1.9.0-dev>@{
  xp.compiler @FileSystemCL<...\xp.thekid.lang\compiler\src\main\php\>
  tests: net.xp_lang.tests @FileSystemCL<...\xp.thekid.lang\compiler\src\test\php\>
}
```