Remove 3/4 of Gradle warnings

[Emkas]

When building a code there is warning:

Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.6.1/userguide/command_line_interface.html#sec:command_line_warnings

I've corrected 3 of 4 problems. For the last one (changing compile for api/implementation/runOnly etc.) I'd need to know a project structure little better.

[harshavardhana]

Please fix build issues @Emkas

6 actionable tasks: 1 executed, 5 up-to-date
Error: Exception in thread "main" java.lang.Exception: version does not match; expected=8.3.4-DEV, got=task ':api:jar' property 'archiveVersion'
	at TestUserAgent.main(TestUserAgent.java:45)
Error: Process completed with exit code 1.

[Emkas]

Hmm... that's strange. I've ran build and functional tests without problems. Sorry for that. I'll look into it.

[Emkas]

OK. I found out about TestUserAgent class. It's funny because this looks like it's connected to a Gradle's bug: gradle/gradle#14972. I've added .get() to this property and on my local machine TestUserAgent works.