source & target = 1.5

Set maven.compiler.source and target to 1.5.
Fixes compilation errors with default maven configuration:


    [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project xtend-annotations: Compilation failure: Compilation failure:
    [ERROR] ...../xtend-annotations/xtend-annotations/src/main/xtend-gen/de/oehme/xtend/annotation/data/ImmutableProcessor.java:[24,1] error: annotations are not supported in -source 1.3
    [ERROR] 
    [ERROR] (use -source 5 or higher to enable annotations)
    [ERROR] ...../xtend-annotations/xtend-annotations/src/main/xtend-gen/de/oehme/xtend/annotation/data/ImmutableProcessor.java:[40,20] error: generics are not supported in -source 1.3