Fixed new version checker to work under linux

* Simplified getJavaVersion()
  Returns JavaInfo object
* LaunchFrame.java and OptionsPane.java:
  Use JavaInfo's getMajor and getMinor instead of unnamed array
* JavaInfo.java and JavaFinder.java: minor edits

RFC: Should Modpack.minJRE be JavaInfo?
     If getMinJRE() and getJavaVersion() both returns JavaInfo object then it's possible to compare those objects directly instead of comparing major and minor elements separately.