Fixes TestUp tests for SketchUp 2013

Removing bugs_fixed/TC_2119710.rb and functional_tests/TC_Picking.rb
because they were using files in lib/ that we never shipped, and will
break in the next version of SketchUp.  A complete refactor is
necessary.  Deletion will cause less confusion IMHO.

functional_tests/TC_BreakEdges2D.rb had no localization and was
barfing, so I removed the $exStrings.GetString

functional_tests/TC_importers_sanity.rb broke because of Mac
Preferences changes, and was overly complicated.  Simplified greatly by
updating dictionary plist items using -dict-add.  Also, a new 2013 bug
requiring a placement of a 3D before it's edges, faces etc… were added
to the model statistics, required similar treatment to skps.

functional_tests/TC_install_from_rbz.rb now uses su_webtextures.rb,
because Examples are no longer installed by default.

ruby_classes/TC_Image.rb needed a little refactor love, and DC's have
moved from Tools to Plugins.

ruby_classes/TC_SketchupExtension.rb requires Examples to be installed,
and now checks for it and raises an exception if with instructions on
how to get it installed if it's not there.