clarify build process

--HG--
extra : rebase_source : 7701e980c010e13487a6e364fcee16b221856a88
extra : amend_source : e8e7df48d1796a20804488cc97c42e2bbe50f5cb
Always pass context when retrieving vpn config, don't try JB+ extra on ICS (closes issue #188)
Update buildToolsVersion to "18.0.1" (closes issue #190)
Fix compiling with Android NDK r9
Update translations
Version 0.5.40
Log error if the IP that should be set is invalid
Guess if a certificate is stored in hardware