Fixes to indexes and constraints to be shown properly in OE

[samir-puranik]

Addresses issues described in microsoft/azuredatastudio-postgresql#452 and microsoft/azuredatastudio-postgresql#453.

• Indexes should now show scripting options regardless of if they are unique or not
• Indexes will not show primary key, but this will show up in constraints. This is following the pattern of PgAdmin
• Constraints should properly show the associated constraints
  1. Check constraints
  2. Exclusion constraints
  3. Index constraints (primary key and unique key)
  4. Foreign key constraints
• Template files were updated for all constraint types