Install if the Eigen from the submodule (3rdparty directory) is used. This is the case, except when a user specifies their own EIGEN3_INCLUDE_DIR - in that case, we don't want to install the headers.

The submodule is the current master, which is exactly v1.2.2.
The removed local copy is v1.1.1.

Files saved with the old version seem to be readable with the new version. (apart from the fact that we've now changed to Eigen, which makes it incompatible to the old models.)

1) Fixes for OpenCV > 2.4.3
2) Update to newest eigne3 cmake file (support in environment variables).

Otherwise, when another project includes eos via add_subdirectory(), these paths will refer to the top-level CMakeLists, not this one from eos.

This was omitted earlier by accident

It is modeled after the vertex shader / fragment shader approach of modern OpenGL.
It also includes a texture extraction fragment shader, which hopefully will replace the current affine texture extraction.

This is still very much experimental, containing lots of todo's. For example it contains lots of if-hacks to select the correct fragment shader (for rendering or texture extraction).

Adjusted all includes, files and bindings.

If 'REQUIRED' used inside 'find_package' there is no need to check '*_FOUND'
variable. And vice versa - if package is not optional then 'REQUIRED' can be
used instead of 'if(NOT *_FOUND) message(FATAL_ERROR)' block.

Let's see if there's ever a "modern CMake" solution for this without a custom target.
target_sources(eos INTERFACE ${HEADERS}) doesn't seem to be a proper solution.

Also swapped order of project() declaration and cmake_minimum_required()

Just test it locally after we're done.

Replaced C++ compiler check logic and replaced the eos custom target with an INTERFACE library target

At the moment this doesn't make the headers show up in IDEs - we'll deal with it later.

Previously, we would just copy the whole folders, which resulted in a quite large install folder. Now we're only copying the headers and the licence files.