Implement proper copy constructor for ResourceManager to allow mesh copying.

Fixes #5.
9 jobs for mesh_copying in 3 minutes and 59 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed clang-c++11 #40211
Linux

00:03:48

passed cppcheck #40213
Linux

00:00:29

passed doc #40218
Linux

00:00:20

passed gcc-c++11 #40210
Linux

00:03:59

passed macos-c++11 #40212
Apple

00:01:27

passed VS2013-32-bit #40217
VS2013

00:00:50

passed VS2013-64-bit #40216
VS2013

00:01:01

passed VS2015-32-bit #40215
VS2015

00:01:01

passed VS2015-64-bit #40214
VS2015

00:01:10