The idea is to keep all declarations in the same packages from Kotlin's
point of view, but use JvmPackageName annotation to move them to another
JVM package, to avoid the split package problem which is otherwise
unsolvable when using module path on Java 9 (KT-19258).

In this commit, kotlin-stdlib-jre7/8 are moved to kotlin-stdlib-jdk7/8
and in the subsequent commit, -jre7/8 are restored. This is done in
order to make Git recognize this as a file move to preserve history.

Include new stdlib-jdkN artifacts in manifest version tests.

Also update links and overall readme structure.