Eliminate dependency on UnstructuredGrid

The only thing it was needed for was the number of cells in the grid,
and the Cartesian dimensions, and those are already available from other
structures.
Explicitly mention template parameter for base class

GCC 4.4 doesn't understand that EclipseHandle (without template
parameter) is supposed to refer to the base class and not a field.
Hide internals in its own namespace

If we put them in the anonymous namespace, then we cannot have a
reference to the types in the header (because that would mean different
things in each compilation unit).
Use integer for counter and cast to enumeration
Avoid comparing signed and unsigned integers
Provide default (move) constructors and operators

C++11 will write a default move constructor that invoke the same in
the base class. However, GCC 4.4 doesn't support this, so we have to
explicitly give the implementation that would be generated on later
compilers.
Refactor common constructor code into a function

GCC 4.4 doesn't handle calling another constructor in the same type.
(Allowed in C++11 but not supported in GCC 4.4's --std=c++0x mode)
Active cell flag is integral, not floating point type
Copy between arrays instead of function call

By getting a pointer directly into the data store, the copy can be
performed faster than calling a function for every item. Also, the
storage type of the array should now match the C++ one exactly (i.e.
no conversion to float).
Document limitations of type parameter for getValue
Don't rely on implicit inclusion
Masquerade the actual output format with an interface

Using an interface allows us to code the simulator to just pass the
necessary state variables to something which implements this, and
then the user can select the actual output format with configuration
values. This allows us to set new formats without having to change
the code being compiled (for instance, we can have a special debug
"format" which prints out things of interest in each timestep)
Reorder loops to resemble future processing

We will look at the presence of keywords first, and then for each
keyword determine which wells it applies to.