Add samples/ directory from OCCT 6.7.1

Subdirectory samples/mfc has been dropped, it is quite large.
Update CMakeLists.txt and NEWS to release OCE 0.16

Bump OCE_ABI_SOVERSION, this version is not binary compatible
with OCE 0.15.
Fix race condition when building with OCE_USE_PCH=ON OCE_COPY_HEADERS_BUILD=ON

See for instance travis build failure for job 257.5.
Merge pull request #515 from tpaviot/review/copy-samples-occt6.7.1

Add samples/ directory from OCCT 6.7.1
Merge pull request #516 from tpaviot/review/fix-travis-pch-copy-headers

Fix race condition when building with USE_PCH and COPY_HEADERS_BUILD
Merge pull request #517 from tpaviot/review/release-OCE-0.16

Update CMakeLists.txt and NEWS to release OCE 0.16
Bumped OCE version number to 0.17-dev
[acc-warning-fix][assignment-operator-unchecked-source]

"operator= does not have a check for the source and destination
addresses being non-identical"
If the source and destination strings point to the same place, then this
will result in undefined behavior (delete[] the ptr and then memcpy()
from it).