Rename javaVersion to jvmVersion

[mbhave]

The java version selected doesn't seem to affect projects generated in Kotlin (and maybe Groovy too).

[snicoll]

This is more than an UI thing. We need to express in the metadata that this field doesn’t make any sense when kotlin is selected

[snicoll]

There is also a related API glitch in the new API. ProjectDescription has a javaVersion property that should not be there in theory with Kotlin.

This is, even more, a problem with the new API as Java is an implementation detail but I don't see concretely how we could fix this atm.

[wilkinsona]

I was going to suggest pushing it down onto JavaLanguage but, judging by the comment on the javaVersion field, I can see you've already considered that.

[snicoll]

I am going to reuse this issue to suggest that the javaVersion field be promoted to a JVM version or something which is what the new API uses.

We should update the metadata in a non backward compatible manner at some point as javaVersion is an advertized concept but I guess we can do that separately.

[snicoll]

paging @mbhave for feedback