Add dependencies using EXCLUDE_FROM_ALL flag

[TheLartians]

Implements #152 by adding all dependencies using the EXCLUDE_FROM_ALL flag by default adding an EXCLUDE_FROM_ALL optional argument. Further testing is required to see this could represent a breaking change for real projects and see if an optional implementation or an opt-out flag would be appropriate.

TODO

• Test in real-world projects
• Decide if should be always on, opt-in or opt-out
• Settle for an API
• Update cmake-format configuration
• Consider edge cases
• Add a unit test

[TheLartians]

After some testing I believe that the option should not be set by default, as even some of my own projects depend on installation of components defined only in outer dependencies. This might not be a best practice, but setting the flag by default could unintentionally break other projects as well. A smoother transition may be achieved by adding an optional flag that may be promoted to default sometime in the future.