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-3474 FIXED crash on startup in LLTextureCache::purgeAllTextures(bool) attempting to delete texture cache

replace llinfos, lldebugs, etc with new LL_INFOS(), LL_DEBUGS(), etc.

Given that third-party libraries (such as Boost) can and do use those names,
properly namespace-scoped, it's unpardonable to break any such innocent usage
with a macro. Given the pervasiveness of the need, introduce a header file
with the requisite #undef directives.

STORM-1476 FIXED Replaced non-fatal errors in LLDirIterator constructor with warnings to avoid viewer crashes.
Added exception handling case.

causing the LLDirIterator to crash the viewer when opening chat logs

STORM-1260 FIXED Replaced llerrs messages with llwarns in directory iterator code to avoid viewer halt when a cache dir is not found.

STORM-1260 FIXED Replaced llerrs messages with llwarns in directory iterator code to avoid viewer halt when a cache dir is not found.

- Added a class implementing directory entries iteration with pattern matching which is used in unit tests instead of LLDir::getNextFileInDir.

STORM-550 FIXED Fixed LLDir unit test which failed for some complex wildcard combinations.