PR: Clarify and polish UI text for Python interpreter pref pane

[CAM-Gerlach]

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)

• Refine the UI text and formatting throughout the pane and dialogs
• Since UMR is on by default, most users will never see the big wall of text that pops up when enabling it. Therefore, move most of the general content to a tooltip and while keeping the rest specific to enabling/disabling it as a pop-up dialog when toggling it
• Remove an obsolete warning that a Python 2 interpreter is used with a Python 3 Spyder, or vice versa. The latter has not been possible for a long time as Spyder only works on Python 3, and at least as of 6.1 (and possibly 6.0 or before), neither is the former as versions of Spyder-Kernels compatible with it only work on Python 3.

Before	After

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: CAM-Gerlach

[ccordoba12]

Just a minor suggestion, the rest looks good to me @CAM-Gerlach.

[CAM-Gerlach]

Rebased this one too just in case

[CAM-Gerlach]

Failed 3 times in a row :(

[ccordoba12]

Thanks @CAM-Gerlach!