fix: better align access keys with the guidelines

[smileyhead]

Summary

Resolves #678.

Based on Microsoft's guidelines, I have…

• added access keys (mnemonics) to all menu items and some buttons which I found were missing them
• moved the position of existing mnemonics where needed
• created new strings where a mnemonic was needed for only one instance of that string
• created new strings specifically in the New Tag window to replace the generic ‘+’ buttons with something more descriptive that allows for mnemonics
• created strings and added labels to the main window drop-downs to allow for mnemonics
• created links (buddies) between labels and corresponding UI elements to allow for mnemonics
• modified the File -> Open Recent list to prefix numbers in front of the directory paths, which allow for mnemonics

Unresolved issues:

• I would have liked to create a mnemonic for the ‘Color’ label in the New Tag window that activates the button below it. The buddy has been defined, but it does not work and I do not know why.
• The search box cannot be added mnemonics to directly and I am unsure on how to proceed (see this comment for more info)
• Some actions (Apply, Delete, Edit, Overwrite, Rename, Skip) have two versions, with the ‘_alt’ versions having access keys defined and the normal versions not. I would advise removing the access key-less variations (especially for Apply and Done).
  • On the other hand, Cancel also has an ‘_alt’ version with an access key that should be removed, as the Cancel action always has Esc hard-mapped as its access key.
  • Similarly, Done should not have a mnemonic, as its function is to just close a window, and so Esc would suffice. (I have taken the liberty to remove the mnemonic from the alt version of this string, since it was conflicting with something else.)

Tasks Completed

• Platforms Tested:
  • Windows x86
  • Windows ARM
  • macOS x86
  • macOS ARM
  • Linux x86
  • Linux ARM
• Tested For:
  • Basic functionality
  • PyInstaller executable

[smileyhead]

While looking into adding mnemonics to the search bar in the main window, I have discovered that adding them to a QLineEdit element directly is, unfortunately, not supported.

We might consider adding a shortcut key to focus on the text box (Ctrl + F, for instance) and signal this in the placeholder text (‘Search Entries ({shortcut})’), but that is out of scope for this PR. Alternatively, we could add a buddied QLabel in front of the search box, something like ‘Search Entries:’, but I do not wish to do that without prior approval.

[smileyhead]

I apologise; I realised I have made this PR too soon, as there are still more commits I wish to make. I will reopen this when I am done.

[smileyhead]

I have made all the modifications I wanted and updated the PR to reflect that. It is now ready for review.