Allow dependencies to be installed inside a .sublime-package

My dependency can be packed inside a `.sublime-package`, there no
need to it be on the loose user packages folder. When I need it, I
just import like:
```python
from DependencyName.file_name import CoolClass
```

packagesmanager/package_manager.py

@@ -1185,9 +1185,11 @@ def install_package(self, package_name, is_dependency=False):
 
             dependencies_path = 'dependencies.json'
             no_package_file_zip_path = '.no-sublime-package'
+            on_package_file_zip_path = '.on-sublime-package'
             if skip_root_dir:
                 dependencies_path = root_level_paths[0] + dependencies_path
                 no_package_file_zip_path = root_level_paths[0] + no_package_file_zip_path
+                on_package_file_zip_path = root_level_paths[0] + on_package_file_zip_path
 
             # If we should extract unpacked or as a .sublime-package file
             unpack = True
@@ -1210,6 +1212,13 @@ def install_package(self, package_name, is_dependency=False):
             if is_dependency:
                 unpack = True
 
+            # If it is a dependency and package maintainer doesn't want a .sublime-package
+            try:
+                package_zip.getinfo(on_package_file_zip_path)
+                unpack = False
+            except (KeyError):
+                pass
+
             # If dependencies were not in the channel, try the package
             if not is_dependency and not have_installed_dependencies:
                 try: