Check in Shell Script if java Version >= 8

[predic8]

To avoid the following error extend the scripts to check Java version and to show warning if Java < 7.

thomas@MacBook-Pro:~/java/membrane/membrane-service-proxy-4.2.2$ ./service-proxy.sh
Membrane Router running...
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/predic8/membrane/core/Starter : Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)