ocl: Change static variable order in cl_context.cpp to avoid crashes during destruction

ContextImpl::currentContext contains a reference to one of the
DeviceInfoImpl objects from:

static std::vector<DeviceInfoImpl> global_devices;

ContextImpl::currentContext is destroyed in the destructor
for the statically defined object __module, and relies on its
DeviceInfoImpl reference to query some hardware features while
being destroyed.

This means that we need to ensure that the global_devices vector is
destroyed affter __module, otherwise ContextImpl::currentContext's
DeviceInfoImpl reference will no longer be valid when __module is
destroyed.

Since these variables are all confined to a single compilation unit,
they will be destruct from bottom to top, so we need to make sure
that __module is the bottom definition so it can be destroyed first.
Merge pull request #3337 from tstellarAMD:2.4-ocl-context-cleanup-fix
iOS: fix crash from overrelease in UIImageToMat
fix installation layout for debian packages:

Install symlinks to shared libraries as a part of development package,
not runtime package.

It is default behavior for debian packages.
Merge pull request #3340 from AdLantis:2.4
viz: fixed memory leak, issue 3961
Merge pull request #3346 from Nerei:fixed_memory_leak_in_viz
Merge pull request #3341 from jet47:deb-package-lib-symlinks
Fix test name.
TIFF loader: Allocate large enough buffer when (bpp * ncn) > 8.
TIFF loader: Pass buffer size to read functions.
Merge pull request #3350 from Trundle:fix_some_tiff_crashes
Merge branch '2.4' of https://github.com/Itseez/opencv into putText_develop2
replace not ascii and not cyrillic symbols with '?';
Merge branch 'putText_develop2' of https://github.com/BKNio/opencv into putText_develop2