PR: Make tour a plugin in the new API

[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 PR is based on #14276

Issue(s) Resolved

Fixes #

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct:

[pep8speaks]

Hello @juanis2112! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file spyder/utils/icon_manager.py:

Line 312:80: E501 line too long (93 > 79 characters)

Comment last updated at 2021-07-04 23:39:10 UTC

[ccordoba12]

Thanks @juanis2112 for your work on this! It looks pretty good so far! I left a bunch of suggestions to remove unnecessary code and some questions for you.

Also, please check if you need to reapply the changes added in PRs #15052, #15067, #15036 and #14420, because those were done after the initial migration PR made by Gonzalo.

[ccordoba12]

Great work @juanis2112 so far! Last comments on my side, then this should be finally ready.

[ccordoba12]

@juanis2112, you forgot to address this comment. I suggest adding mdi-map-outline to the icon_manager dict with the tour key, and using it here.

[ccordoba12]

Also, please remove the file spyder/app/tour.py in this PR, because it's not needed anymore.

[ccordoba12]

Thanks a lot @juanis2112 for this. You did a great work on this PR!