Added some more printouts when Overviewer is first starting

Often, when people ask questions about Overviewer, "all it says is
'Welcome to Overivwer'" is a common question.  Enable a little more
logging info at the start of Overviewer to hopefully make it more clear
that something is happening
Remove SizeOnDisk from table of detected worlds

This fields hasn't been properly filled in for many many releases.
We could detect this value some other way, but i'm not sure the value in
doing this
The previous Google Maps URL was 404'ing. New URL added.
Merge pull request #1071 from urda/fix-terms

The previous Google Maps URL was 404'ing. New URL added.
--check-tiles note about overestimating

added note about --check-tiles overestimating tiles and remaining processing time
Merge pull request #1078 from jasendorf/patch-1

--check-tiles note about overestimating
New blocks for snapshot

Granite, Diorite, Andesite (new data values for blockid:1)
Iron trapdoor

See #1062
New snapshot block: slime blocks

See #1062