Implement proper copy constructor for ResourceManager to allow mesh copying.

Fixes #5.
9 jobs for mesh_copying2 in 3 minutes and 47 seconds
Status Job ID Name Coverage
  Test
passed #40422
VS2013
VS2013-32-bit

00:00:54

passed #40421
VS2013
VS2013-64-bit

00:00:57

passed #40420
VS2015
VS2015-32-bit

00:01:13

passed #40419
VS2015
VS2015-64-bit

00:01:11

passed #40416
Linux
clang-c++11

00:02:22

passed #40418
Linux
cppcheck

00:00:43

passed #40423
Linux
doc

00:00:23

passed #40415
Linux
gcc-c++11

00:03:47

passed #40417
Apple
macos-c++11

00:01:29