Merge branch 'private-cloning-constructors' into 'master'

Make some *PropertyT constructors private to prevent accidental misuse.

See merge request !31
11 jobs for master in 3 minutes and 48 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #52620
VS2013
VS2013-32-bit

00:00:55

passed #52619
VS2013
VS2013-64-bit

00:00:56

passed #52618
VS2015
VS2015-32-bit

00:01:18

passed #52617
VS2015
VS2015-64-bit

00:01:07

passed #52616
VS2017
VS2017-32-bit

00:01:11

passed #52615
VS2015
VS2017-64-bit

00:01:32

passed #52612
Linux
clang-c++11

00:03:26

passed #52614
Linux
cppcheck

00:00:46

passed #52621
Linux
doc

00:00:19

passed #52611
Linux
gcc-c++11

00:03:46

passed #52613
Apple
macos-c++11

00:02:49