Add pcl version check for letting users know the version issue

[LimHyungTae]

Hi Koide, this is Hyungtae.

I added a version check line, so if a user turns on the PCL option (i.e., set BUILD_WITH_PCL ON), CMakeLists.txt automatically checks the PCL version and then rejects the build once the satisfaction of the PCL dependency does not meet as follows:

Please check it.

Cheers!

[LimHyungTae]

If your desktop has PCL 1.11.0, then please test it whether it works or not.

[valgur]

Can be simplified to just

Suggested change

	find_package(PCL REQUIRED)
	if(PCL_VERSION VERSION_LESS "1.11.0")
	message(FATAL_ERROR "The found PCL version ${PCL_VERSION} is too low. Required is at least 1.11.0")
	endif()
	find_package(PCL 1.11.0 REQUIRED)

[LimHyungTae]

So nice, @valgur, but if so, what if one uses PCL 1.12. or more higher version?
Plus, it's my personal question, but I'm curious whether it is possible to install multiple PCL versions on a machine. Thx!

[koide3]

@LimHyungTae
Thanks for your contribution. The way suggested by @valgur only specifies the minimum required version and should accept newer versions.

Possibly you can switch different PCL versions with some cmake arguments. But, I'm not very familiar with the way handling multiple versions of a library in cmake.