update library dependencies and remove some sample app cruft

Pruned out some cruft in the widevine sample apps. 

Brought the gradle plugin back up to 0.11.+ to be able to use Android Studio 0.6.1 effectively.

Pulled the library path out into a gradle variable to be set as desired. Currently defaulted to <user home directory>/libs
I disagree that it's bad form, but I wouldn't mind if we chose something else like /tmp/libs.  On the build server, the directory needs to be outside the cloned repo, because that gets deleted and recreated for each build.  Another option would be to use a directory inside the repo by default via a property in gradle.propeties and then the TeamCity scripts can override that property to point at a directory in the build user's home directory.