move to gradle 2.3 and compile at catkin_make

[talregev]

• move to gradle 2.3
• add excludes to compile with catkin_make
• remove buildscript.gradle. it better to add two line to main project, because android-studio will notice when you change them and let you decided if you want to compile it again. otherwise the android-studio will not notice the changes in spepreate file.
• remove dummy tasks at docs
• change to cleanDocs task, clean already taken.
• can add now any subproject, not neet start with android_*

[rking788]

+1