Update README.md samples

[stefan-niedermann]

• Combine samples for Activity and Fragment - they are nearly identical and the duplication make everything quite complicated
• Update samples to use var keyword - makes it easier to focus on the actual stuff
• Update samples to use the less verbose constructor of NextcloudAPI without explicit ApiConnectedListener callback (see Make NextcloudAPI constructor less verbose #400)
• Remove <queries> section. This can be omitted, since it is part of SSO lib 0.6.0 (see Add queries to Manifest so that lib can find Files App for SDK>=30 #282)

Signed-off-by: Stefan Niedermann info@niedermann.it

[tobiasKaminsky]

* Update samples to use `var` keyword - makes it easier to focus on the actual stuff

This only works for Kotlin, right? But all samples are in Java?

[stefan-niedermann]

No, this is a Java 10 feature and we are using Java 11 🙂