efl: Add Efl.Version struct and APIs

efl: Add Efl.Version struct and APIs

The original idea behind knowing the app's version of EFL is not
a great story. It comes from the fact that some bugs exist in
earlier versions of EFL, and some things need to be fixed. But
those fixes may break behaviour for older apps. This patch is
opening the way to the slippery slope of bug compatibility.

Unfortunately this is a requirement if we want to be able to move
forward and not break apps when we fix bugs (behaviour or ABI).

I hope we will not need to implement too many (if any) workaround
such issues. For now, this will only be used as debugging info.

EFL_MAIN() and ELM_MAIN() will both set the app's EFL version
automatically at startup time. Some internal helpers can be added
later to check how the app build-time and run-time version of
EFL differ.

@feature