Don't add show_advanced_fonts control if theme doesn't define them

[NateWr]

This prevents the little checkbox to show or hide advanced font options from being added to the customizer when the theme does not have any advanced options defined.

[NateWr]

I went ahead and pushed another commit onto this PR just to bypass any merge conflicts from submitting two simultaneous PRs.

The second commit adds support for a default_title attribute when specifying default fonts. I feel like the long font stack string might be confusing for users and this gives me the ability to simplify things.

If you don't want the default_title support you can just cherry-pick the other commit in as desired.

[christianc1]

Sweet, thanks @NateWr. I'll review asap and update the PR.

[NateWr]

Sorry for overloading this PR with different things, but I added one more commit to it which seems like a no-brainer.

[NateWr]

Just touching base on this. Anything else you need from me?

[christianc1]

Hi @NateWr, sorry we sort of left you in limbo. We're really busy on some other projects but I'll take some time next week to review the PR and let you know. Until then,I'd recommend just pushing your fork up to your deployment if you haven't already. Thanks again for contributing, I'll definitely be in touch next week.

[NateWr]

No worries!