Fix postfix templates regarding for loops to be consistent with index

[jjohnstn]

• use ${index} in templates everywhere the index is accessed
• fixes result of fori postfix is strange #299

What it does

Makes the for, fori, forr postfix loops use just one variable name for the indexing instead of mixing generated name and i.

How to test

Create a method that passes an array of String[] args
Type args.fori and do postfix completion. The name used for the index should be the same as the variable used in the test of
the forloop.

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)