Fix sharp corners on placeholders

[flofriday]

Description

All placeholder now have round corners matching the corner radius of the image that will eventually load.

I also added placeholder to the avatars on the contributor screen.

Screenshots (now/earlier):

Checklist

• I have read the contribution guidelines: https://github.com/AntennaPod/AntennaPod/blob/develop/CONTRIBUTING.md#submit-a-pull-request
• I have performed a self-review of my code
• I have run the automated code checks using ./gradlew checkstyle spotbugsPlayDebug spotbugsDebug :app:lintPlayDebug
• My code follows the style guidelines of the AntennaPod project: https://github.com/AntennaPod/AntennaPod/wiki/Code-style
• I have mentioned the corresponding issue and the relevant keyword (e.g., "Closes: #xy") in the description (see https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue)
• If it is a core feature, I have added automated tests

Notes

I am quite interested in hearing some feedback about my code here. Like, I know that the GradientDrawable I used here seems somewhat questionable since we don't need a gradient. However, I couldn't get ColorDrawable to round the cornors and the ShapeDrawable and PaintDrawable were always transparent :/

Also another question, I initially used quite a few type inference assignments with var x = new SomeClass(). However, after double checking I discovered that the rest of the codebase isn't written in that style so I removed them again. So I wanted to ask again if there is a special reason why they aren't used and would you be against introducing them?

[ByteHamster]

Thanks! Will be released in 3.5.x

I know that the GradientDrawable I used here seems somewhat questionable since we don't need a gradient. However, I couldn't get ColorDrawable to round the cornors and the ShapeDrawable and PaintDrawable were always transparent :/

I don't know. In my quick experiment with ShapeDrawable, they were transparent as well.

I initially used quite a few type inference assignments with var x = new SomeClass(). However, after double checking I discovered that the rest of the codebase isn't written in that style so I removed them again. So I wanted to ask again if there is a special reason why they aren't used and would you be against introducing them?

I think because it is a Java 10 feature, it might not be supported on Android. In any case, personally, I find it easier to review code when I can see the types of things. Especially when reading the code on GitHub (or any other diff tool) where there is no IDE to annotate the types. Maybe relying so much on the types and not using the new automatic stuff makes me a bit old-fashioned :D Maybe that's also because at work I sometimes work on c++ projects that use so many templates that the IDE cannot figure out what type everything has -- then I have no auto-completion when someone uses auto instead of specifying the type explicitly.