android: remove duplicates from uavo hash list

Fixes make warnings when the uavo hash list contains duplicates.

Useful in the future when generated lists of hashes may have
duplicates.
android: force java source/target versions to 1.6 with java7 and java8

This avoids error messages during android build:
  bad class file magic (cafebabe) or version (0034.0000)

when using java7 or java8 to compile the android app.
Merge pull request #959 from solidgoldbomb/fix-android-java-1.7+

Fix android java 1.7+