Add tooltips to playback controls

[rmg-x]

Small change to add tool tips to the playback controls.

[xou816]

Hi there, thanks for the PR! Quick review from my phone: I think the tooltips for play and pause are not translated?

[rmg-x]

That's correct, I guess I should've asked before adding the "translatable" attribute.

Does text like this need to support a certain set of languages (other than English) before being merged, if any?
If not, should the translatable attribute be removed?

[rmg-x]

Oh, and I forgot to ask about the code portion of the text generation (which I think you were referring to originally):
What method/pattern is typically used to get translated text via the code if applicable?

[xou816]

This project uses GNU gettext; anytime you need a string from source code to be translated, wrap it in a call to the gettext macro or fn, you'll see multiple instances of it throughout the code.

Then you can run the meson commands mentioned in the README to extract these strings (as well as the strings marked as translatable in the ui files): they will be added to all currently supported languages but will be blank initially and will fallback English, but people will be able to contribute translations from there :)

[rmg-x]

Ah okay, that makes sense, thanks!
I've made some code changes and included screenshots below. Let me know if everything looks alright.

[xou816]

LGTM, thanks for your work, merging! :)

[xou816]

On second thought, I merged this a bit fast, maybe the tooltip for the Repeat button could use some improvement since it switches between three different "modes", but no big deal obviously :)

[rmg-x]

Ah, good point. I completely forgot about that as I don't use that button often.
It looks like the current functionality Spotify has is to display the next "state" in the tooltip text.

Example:

• Disabled -> "Enable repeat"
• Enabled -> "Enable repeat one"
• Repeat(1) -> "Disable repeat"

If I find some more time, I will open a PR if someone else hasn't already.