Change: Clean up window title and button capitalization and wording

[2TallTyler]

Motivation / Problem

Knock knock, it's the grammar police!

Not really, but while reviewing #10541 I tried to ensure its new windows and button matched our current precedent, and discovered that our current precedent is a bit messy. Not totally random — we have some reasonably consistent rules — but with enough outliers for it to be frustrating.

Description

Let's clean up the easy outliers and make them match the pattern we've generally established:

Generally title case unless they're a sentence fragment:

• Window captions (titles)
• Buttons

I reworded the easy sentence fragments and left the tricky ones alone for later (or never 😛).

Always (to my knowledge) sentence case:

• Dropdown options

I also fixed some confusion with AI and GS setting windows, where all the buttons say "settings" but the windows themselves say "configuration". I went with "settings" because our use of the synonyms "options" and "settings" is confusing enough without adding "configuration" to the list. 😃

I made a bunch of commits for reviewers to easily follow, will squash when merging.

Most likely supersedes #9118.

Limitations

• As mentioned above, I left some window captions as sentence fragments for later/never because they're troublesome and include more information than we can fit in a title-style caption.
• Translators have to do more work.
• I did not change string names; none seemed particularly problematic to me.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker