After review and testing, realized that 'WatchdogEnabled' is actually true to its name, and is a boolean, not a timeout value. 'MainloopTimeoutDefault' is the actual timeout value.

Updated descriptions and values accordingly to set Watchdog timeout to 60 seconds.

By the way, moved estate info storage from the REGION/ESTATE floater to a model class.

Watchdog timeout now set to 60 seconds for long-term use (instead of 20, used during crash pile-on).
Updated setting description field to describe how setting the value of WatchdogEnabled will affect Viewer behavior.

(per Monty code review)
The notion of storing LLMemoryInfo data both as an LLSD::Map and an
LLSD::Array of pair arrays arose from a (possibly misguided) desire to
continue producing stats output into the viewer log in the same order it
always used to be produced. There is no evidence that anyone cares about the
order of those stats in the log; there is no other use case for preserving
order. At Monty's recommendation, eliminate generating and storing the
array-of-pair-arrays form: directly store LLSD::Map.

STORM-1482 The Viewer shouldn't overwrite the crash behavior settings, some cleanups to the crash reporters, and the ability to use --set GroupName.SettingName to set parameters outside of the (default) Global settings group.