Improve comprehensibility and consistency of window placement mode names

Summary:
Right now a few of the window placement modes suffer one or more of the following problems:

• Inconsistency between the text shown in the Window Behavior and Window Rules KCMs
• Title does not indicate what it does
• Awkward wording
• Lack of unity in grammatical mood between the different modes

This patch fixes these issues by improving the strings and standardizing on the descriptive mood:

• Smart -> Minimal Overlapping
• Maximizing -> Maximized
• Cascade -> Cascaded
• Zero-Cornered -> In Top-Left Corner

Strings are also unified between the window behavior and window rules KCMs, and docbooks are adjusted accordingly.

Test Plan:

Reviewers: KWin, VDG, ndavis, filipf, zzag, romangg

Reviewed By: KWin, VDG, ndavis, filipf, romangg

Subscribers: gladhorn, alexeymin, IlyaBizyaev, broulik, hein, hpereiradacosta, GB_2, alexde, davidedmundson, romangg, cfeck, filipf, zzag, ndavis, kwin, kde-doc-english

Tags: KWin, Documentation

Differential Revision: https://phabricator.kde.org/D23415