Assert-Module: Reduce verbose output

[johlju]

Pull Request (PR) description

• Assert-Module
  • Now it possible to forcibly import a module using -ImportModule -Force
  • It no longer outputs verbose messages that is normally generated when
    using Get-Module -ListAvailable if the module that is asserted is
    already in the session (issue Assert-Module: Outputs unnecessary verbose statements due to -ListAvailable is used each time  #66).

This Pull Request (PR) fixes the following issues

• Fixes Assert-Module: Outputs unnecessary verbose statements due to -ListAvailable is used each time  #66

Task list

• Added an entry to the change log under the Unreleased section of the
  file CHANGELOG.md. Entry should say what was changed and how that
  affects users (if applicable), and reference the issue being resolved
  (if applicable).
• Documentation added/updated in README.md.
• Comment-based help added/updated for all new/changed functions.
• Localization strings added/updated in all localization files as appropriate.
• Examples appropriately added/updated.
• Unit tests added/updated. See DSC Community Testing Guidelines.
• Integration tests added/updated (where possible). See
  DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[johlju]

@PlagueHO when you have time can you review this one. There is no hurry.

[gaelcolas]

Only found one typo. Feel free to merge.