Peter M. Groen / openbr

This allows e.g. writing .mat files as directly as output of compare, as well
as writing similarity matrices as images (although this could use some scaling)

Signed-off-by: caotto <ottochar@gmail.com>

Export the facevacs directory found by cmake, use that to define a default
config file location of facevacs_dir/etc/frsdk.cfg. Store the config file
path as a property of Globals, allowing users to specify a config file path
as a command line argument to br.exe.
Modifications to openbr_plugin.cpp allow adding dynamic properties (strings
only) to br::Objects.

Target version 8.6.0 of the sdk (this could stand to be generalized somehow)
Link debug versions of the library when building debug configurations.
When building with visual studio, pick the appropriate pre-complied library
for the version of the compiler being used.