move gtest into its own VS-specific source-group
move gtest into its own VS-specific source-group

Signed-off-by: Kim Kulling <ab1850e765cb36d3d392c95b68ac3e34036b2afe@googlemail.com>

FredrikHson/openddl-parser,kimkulling/openddl-parser,FredrikHson/openddl-parser,kimkulling/openddl-parser,FredrikHson/openddl-parser,FredrikHson/openddl-parser,kimkulling/openddl-parser,kimkulling/openddl-parser