Rework examples directory

[blnicho]

The pyomo examples directory needs to be cleaned up for consistency and for inclusion in testing.

[franktoffel]

Also, pyomo.org web and PDF docs are referred to the 4.1 version. Not sure if there is backwards compatibility but seems confusing.

[mrmundt]

Potentially problematic examples:

• examples/pyomo/p-median/solver1.py - two unknown imports
• examples/pyomo/p-median/solver2.py - two unknown imports
• examples/pyomo/quadratic/example3.py - use of xrange; might need to be replaced with range?
• example/pyomo/draft/api.py - I don't even know what's going on in here
• doc/OnlineDocs/src/scripting/doubleA.py - ???
• doc/OnlineDocs/src/scripting/Z_init.py - ???
• doc/OnlineDocs/src/scripting/NodesIn_init.py - ???