This reverts commit 681298dd, reversing
changes made to 323f41f4.

This set of changes reverts the merge with master (git revert c83e740e) and results in a version of the DRTVWR-519 that matches what was presemt before it was deployed as a release viewer *plus* 3 small fixes from Maxim (See commits).  This branch can now be used for additional fixes before eventually being used to release D-519 as normal

This reverts commit e61f485a, reversing
changes made to 00c47d07.

The folder where the disk cache lives was originally renamed from llvfs to llcache but @henri's suggestion that that doesn't reflect the other files in the same place and it should be llfilesystem is a good one so I changed it over

First part of change to remove LLVFS from the Viewer. Consists of code changes to remove LLVFS and LLVFSThread classes along with the associated source files. The existing llvfs folder is renamed to llcache. Also includes changes to CMake script in many places to reflect changes. Eventually, llvfile source file and class will be renamed but that is not in this change.

MAINT-4532: properly detect Windows 10 in the 64bit build (only - 32bit runs in Windows 8 compatibility mode)

MAINT-5687: Remove old webkit from the make files and the repo.  Ensure that it is no longer meaningfully referenced.

Remove legacy udp script upload methods,
Refactor script runtime perms from three arrays to one struct array so we don't have to juggle array order anymore.

Now that the viewer's own background updater logic is responsible for
downloading a new installer, the only functionality we still use in
linux-updater that couldn't be expressed more simply in bash is the UI. But
since most Linux distros capable of running SL at all have zenity, and all
will have xmessage, we can handle even the UI part. Add xmenity wrapper script
so update_install doesn't have to care which is present, and make the bash
script that used to launch linux-updater do the real work.

Remove mac-updater subtree from viewer source, along with the
update_install bash script that invoked it. Remove all mention of mac-updater
in CMakeLists.txt files and in viewer_manifest.py.
Change Mac update_install bash script references in viewer_manifest.py and in
llupdaterservice.cpp (which invokes it) to new Python update_install.py.
Add update_install.py, messageframe.py (which puts up some Tkinter UI) and
janitor.py (cloned from vita, it's exactly what we need here).

Building headless and non-headless libraries side-by-side, removing the need for the BAKING cmake setting.