Add support for building with jdk7

Here is a simple pull-request to be able to build the application using the jdk-7.
This fixes the issue reported during install:

install:
     [exec] 4760 KB/s (331172 bytes in 0.067s)
     [exec] 	pkg: /data/local/tmp/ti5x-release.apk
     [exec] Failure [INSTALL_PARSE_FAILED_NO_CERTIFICATES]