Refactor project and platform services

We need this refactoring in order to reuse code for `iOSProjectService`
No, it isn't. This method is deleted in the next PR :) https://github.com/NativeScript/nativescript-cli/commit/a95e45f509ab4a7d8ed436ad3ba32087b1f13db1#diff-b0e2f35593c6b1fd611d1f4dff096f4dL145