User interface updates

[gmossessian]

This PR implements the changes to the user interface suggested in #9 by user @piiit-creates https://github.com/piiit-creates.

I have updated those changes with the latest changes to master.

[acspike]

Thanks for doing this @piiit-creates and @gmossessian. I've had it in mind to do a user interface update for a while, but I'm pretty much fully scheduled out through 2024.

I like the new look, but I see a few glitches that I would like to sort out before I accept the pull request. As I mentioned above, It will be a while before I have time for this. But here's my list, just in case you have the time:

• Normal Mode / Scale Length / Individual: this probably shouldn't show up according to the directions at the top and when it does show up it exposes some of the help text without clicking the help button.
• Normal Mode / Scale Length: the title after the buttons is a little tight, could use additional spacing.
• Normal Mode / String Spacing: the purportional button could be shortened so that it doesn't need to wrap
• Normal Mode / Fretboard Overhang: the tables are tight to the buttons and could use additional spacing, also some of the tables overflow the container.
• Normal Mode / Download as file: we should add a note about disabling print scaling for multipage pdfs. This is the most common issue that I'm contacted about.
• Normal Mode / Download: additional filetypes still appear below but are unstyled.
• Extended Mode / Calculation Method / Scala: the scale file text is indented in the textbox.

[gmossessian]

@acspike thank you for the review.

I am busy with a cross-country move now but intend to come back to this soon -- please keep the PR open.