Invitations for component sharing to other project

**Is your feature request related to a problem? If so, please describe.**

Many projects, especially Open Source ones, use libraries which may also have their own translations, possibly also on Weblate. If these libraries output anything to the screen, the project wouldn't truly be translated. It would be helpful to be able to more easily point contributors to these projects as well.

**Describe the solution you'd like**

Add "External" components to a Weblate project, that link to dependant projects. These may or may not be on Weblate.

**Describe alternatives you've considered**

Using Translation instructions, but this does not seem nearly as clear.

**Screenshots**

I've created a very quick mock-up showing my idea. In this example, "Dependant library" will link you to the other library to translate.

**Additional context**

I am willing to try to work on this myself during Hacktoberfest, if this feature is wanted.