Fix build break with elm_web since 4664b183e

Maniphest Tasks: T1482
autotools: Added elementary-cxx.pc.in.
autotools: Removed useless instruction from Eolian++ helper
tests: Clean-up elementary-cxx test suite.

Removed unnecessary includes.
Added missing bindings.
Added extern "C" guards.
examples: Remove a warning during release compilation.
pkg-config: Brought latest "echo compatibility" changes from EFL to m4/efl.m4.
lib/autotools: Added Elementary.hh.
autotools: Simplified src/lib/Makefile.am quite a bit.

Introduced new .eo lists avoiding redundancy. Create targets to install
generated C++ bindings.