added unit tests for lltrace

made getPrimaryAccumulator return a reference since it was an
always non-null pointer
changed unit conversion to perform lazy division in order to avoid truncation
of timer values

continued conversion to units system
made units perform type promotion correctly and preserve type in arithmetic
e.g. can now do LLVector3 in units
added typedefs for remaining common unit types, including implicits

added convenience types for units F32Seconds, etc.

SH-4346 FIX: Interesting: some integer Statistics are displayed as floating point after crossing region boundary
made llerrs/infos/etc properly variadic wrt tags
LL_INFOS("A", "B", "C") works, for example
fixed unit tests
remove llsimplestat

moved object cache sampling code so that it actually gets executed
default values for stats are NaN instead of 0 in many cases

there are no samples during the time period.
added hasValue to SampleAccumulator so we don't print a value when we don't have
a single sample yet
added some disabled log output for scene load timing

fixed normalization assertions to work with megaprims
added is_zero() utility function
fixed unit declarations to be more clear
fixed texture cache hit rate always being 0

various fixes to lltrace
start() on started recording no longer resets
fixed various instances of unit forgetfullness in lltrace
recording split now has gapless timing
scene monitor now guarantees min sample time
renamed a bunch of stats
added names to debug thread view on windows

also, removed LLTrace::init and cleanup
removed derived class implementation of memory stat for LLMemTrackable
is automatic now

fixed some lltrace logic errors
more consistent syncing of timestamps of sample values in recording stack
selection of primary buffers was completely incorrect
assignment of recordings got wrong play state due to implicit
operator = defined in base class
fixed asset stats only working up to the first send

pulled swap() out of ui time block
cleaned up internal lltrace dependencies, factored out common accumulator definitions