DRTVWR-447: Add (some) metadata to Mac crash reports.

This required reordering certain operations during Mac viewer startup. Split
llappviewermacosx.cpp's initViewer() function into constructViewer() (which
instantiates LLAppViewerMacOSX) and initViewer() (which calls
LLAppViewerMacOSX::init()).

llappdelegate-objc.mm's applicationDidFinishLaunching override now calls
[BugsplatStartupManager start] between constructViewer() and initViewer(): we
want constructViewer() to have set up the logging subsystem so we can log the
actions of BugsplatStartupManagerDelegate override methods, but otherwise we
want BugsplatStartupManager in place as early as possible to catch any early
crashes. Besides, initViewer() ends up overwriting the static_debug_info.log
on which we depend for the *previous* run's crash metadata.

Move the code that initializes the pathname of the static_debug_info.log file
from LLAppViewerMacOSX::init() to the LLAppViewerMacOSX() constructor, since
BugsplatStartupManagerDelegate override methods need to read (the previous
run's) file.

Add code to applicationLogForBugsplatStartupManager override to set new
BugsplatMac 1.0.6 properties userName and userEmail.

Don't log empty fields from static_debug_info.log if we couldn't read it.