PR: Add a new light theme for the interface

[juanis2112]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

This implements light theme from qdarkstyle instead of the OS light theme

It also fixes some minor details with colors:

Issue(s) Resolved

Fixes #

Affirmation

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and understand I am releasing the same under Spyder's MIT (Expat) license.

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Juanis2112

[ccordoba12]

Thanks a lot @juanis2112 and @isabela-pf for your hard work on the new light theme!! It's so cool to finally have it!