DS Classic Menu: Draw calendar and top-bar datetime using monospaced characters

[mentusfentus]

What's changed?

Added support for rendering monospaced text to quickmenu's font renderer. With this, I was able to:

• Increase spacing in calendar's year & month text, resulting in higher DS menu accuracy!
• Fix a minor top-bar issue where its date and time text's position would vary on certain times because of variable text width.

While at it, I also did some slight refactoring of date.cpp to remove redudant code.

Where have you tested it?

melonDS 1.0 RC

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Pull Request status

• This PR has been tested using the latest version of devkitARM and libnds.