Table Columns implementation

[nvarscar]

User story
As a DBA I want to be aware of table columns in the table and manage them via pgmob so that my productivity improves!

Acceptance Criteria

• Tables should have a Columns attribute that contains a Collection of columns
• Each column should have all the attributes necessary to provide enough information for a table.script() operation. This should include
  • data type
  • defaults
  • nullability
  • order
  • generated clause
    • including sequence options
  • statistics
  • collation
• Adding/dropping columns should be possible similar to how other collections behave