[apps][fix] Make examples compilable in Visual Studios 2017 and 2019

[topin89]

Changes are tiny:

• app\frame_grabber added to includes path
• RPLIDAR_SDK_VERSION macro now separated from quotes with spaces, so compiler don't confuse it with string literals
• #include <string> added to stdafx.h in frame_grabber

[bitmeal]

I would like to bump this PR and stress the importance!
The above mentioned modifications are vital to get the sdk and examples building in current versions of VS.

Per my experience and, the necessary adaptations can be reduced to:

• app\frame_grabber added to include path of lidarmgr.cpp
• RPLIDAR_SDK_VERSION macro now separated from quotes with spaces, so compiler don't confuse it with string literals
• #include added to stdafx.h in frame_grabber does not seem necessary

[LFBFerreira]

Thanks for this! I'm trying to create a VS C++ project with this SDK and openFrameworks. And its working in VS 2019 👍