PR: Add Matplotlib as optional dependency for the IPython Console.

[dalthviz]

Pull Request Checklist

• Read and followed this repo's Contributing Guidelines
• Based your PR on the latest version of the correct branch (master or 3.x)
• Followed PEP8 for code style
• Ensured your pull request hasn't eliminated unrelated blank lines/spaces,
  modified the spyder/defaults directory, or added new icons/assets
• Wrote at least one-line docstrings for any new functions
• Added at least one unit test covering the changes, if at all possible
• Described your changes and the motivation for them below
• Noted what issue(s) this pull request resolves, creating one if needed
• Included a screenshot, if this PR makes any visible changes to the UI

Description of Changes

Add Matplotlib as optional dependency of the IPython console (therefore showing it at the dependencies dialog).

Issue(s) Resolved

Fixes #6887