Add show methods for FlatVar and Metadata

[ph-kev]

The show methods can reuse the code for the show methods for OutputVar.

[Sisira07]

Hi! I'm currently working on this, and would like clarify some things related to the display.
Currently this is the format of display for OutputVar:
-Attributes
-Dimension attributes
-Data defined over

I'm considering the following when displaying FlatVar:
-flat_var.data (that is the 1D vector produced by flatten)
-Attributes

As for metadata, i assume to format would be same as OutputVar.

Kindly let me know if any modifications are required!

[ph-kev]

I haven't thought too much about this issue. The current usage of FlatVar in CliMA is to have a standard way to create a 1D vector from a OutputVar that you can use in other applications. When I first made this issue, I was just planning to reuse the show method already defined for OutputVar to define it for FlatVar. I think for now it would be okay to just display the same information as a OutputVar, but I am concerned that it could be confusing.