Deal with unsupported target options in compiler preferences

[iloveeclipse]

After we dropped support of Java < 1.8 compliance level, we still have to deal with projects that have these setting stored in preferences.

• Make sure we don't allow use unsupported compliance from JRE < 1.8
• Make sure we update value of compliance/source and target to first supported version

See https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/1465

[iloveeclipse]

Before change

Considering existing Java 1.7 project settings, following will be shown and after "Apply" all values would be set to 1.7 (even if they show 1.8):

After change Considering Java 1.7 project settings, following will be shown and after "Apply" all values would be set to 1.8 (as expected):