Add some test cases for partial brush and entity selection.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Intermediate commit

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Remove nested pointers for better compile times.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>