[#176] Rename `concat'` expression in Indigo

Description

Problem: Indigo has a concat expression to concat 2 values and concat' to concatenate a list of values. We want to keep concat since it has an equivalent to Michelson's CONCAT. However, concat' can be confusing, it is better to rename this.

Solution: Rename concat' to concatAll.

Related issue(s)

Resolves #176 (closed)

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