[#199] `concatMap` type change

[DK318]

Description

Problem

At this moment concatMap is exported from Data.Foldable but we prefer using Container rather than Foldable.

Solution

Removed export of concatMap and made concatMap function with type concatMap :: Container c => (Element c -> [b]) -> c -> [b].

Related issues(s)

• Fixes #199

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