Update text and images in Lesson 4.3 "Classification"

[Codym48]

Give Lesson 4.3 similar scrubbing to what Lesson 4.2 received in #5463:

• Update missing GUI options (Column) to represent their new name (Value)
• Update images to reflect QGIS master branch (3.13+)
• Remove steps and images for removing borders from landuse layer polygons since they were already removed in Lesson 3.2
• Switch from bulleted lists to numbered lists
• Do not use [periods] after list items that only contain a single simple sentence
  • Still use : after a simple list item that's immediately succeeded by an image
• Update description of ``, :kbd:, and :file: in How to use this tutorial
• Use :sup: formatting for button popup text

I think this warrants:

• Backport to LTR documentation is required

[Codym48]

Two related questions:

1. Are we ok leaving all of the text blocks like "These filters are exclusive..." 3-spaced over rather than left-justified? This is required to continue the list numbering below (15.) instead of starting over (1.)
2. Should "Click and drag this criterion to the top of the list" end with a period in the new approach? It now has additional text just beneath it.

Old approach

New approach

[DelazJ]

Are we ok leaving all of the text blocks like "These filters are exclusive..." 3-spaced over rather than left-justified? This is required to continue the list numbering below (15.) instead of starting over (1.)

It's clear that "Apply the symbology" should be part of the steps so "these filters ..." needs to be indented.
Given that the "these filters.." is about the three previous steps, explaining how they behave, another approach can be to consider rule addition as a whole, ie

1. Add a set of rules as follow: (<== replace with whatever you like)

   1. Add a new rule "landuse" <> 'residential' AND "AREA" >= 605000 and choose a mid-green color
   2. Add another new rule "name" = 'Swellendam' and assign it a darker grey-blue color in order to indicate the town's importance in the region
   3. Click and drag this criterion to the top of the list.

   These filters are exclusive, in that they collectively exclude some areas...

2. Apply this symbology.

Should "Click and drag this criterion to the top of the list" end with a period in the new approach? It now has additional text just beneath it.

Yes, imho

[havatv]

Looks good. Thanks!

[DelazJ]

Update missing GUI options (Column) to represent their new name (Value)

Regarding backports, this is 3.12+