Bump to 1.7

Change-Id: I1fe662814a1c10ac392ce77002f0b63383716ac3
Reviewed-on: http://gerrit.dmdirc.com/2700
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>

nbproject/project.properties

 javac.compilerargs=
 javac.deprecation=true
 javac.processorpath=${javac.classpath}
-javac.source=1.6
-javac.target=1.6
+javac.source=1.7
+javac.target=1.7
 javac.test.classpath=${javac.classpath}\:${build.classes.dir}
 javac.test.processorpath=${javac.test.classpath}
 javadoc.additionalparam=