fixed build warnings

Fixed build warnings

No target runtime definition

[WARNING] No explicit target runtime environment configuration. Build is platform dependent.

This error was caused by tycho not having <enviroments> property specified in it's configuration. It requires to specify the target as a triple <os>, <ws>, <arch> which stand for operating system, windowing system, proccessor architecture.

The same p2 repository URL associated with different declared repositories

p2 repository with URL http://download.eclipse.org/releases/2021-06 is associated with multiple IDs; was 'mars', now is 'neon'

It was caused by using the same <eclipse-site> property to specify repository URL for several different profiles. I opted to just assign corresponding p2 repository url to each defined repository.

Missing maven version

'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing.

This was caused by not specifying maven version.

Not specified java version

I have also noticed an error, message:

bootstrap class path not set in conjunction with -source 8

It was caused by not specifying java version. As I noticed maven already made assumptions about jave version being 8. It is most probably coming from the MANIFEST.MF file, but I am not entirely certain. Anyway, changing it into some newer release should most probably be a matter of another issue.