Removed com.madgag.spongycastle:prov dependency
Created by: williamdes
I removed the com.madgag.spongycastle
dependency to reduce the number of dependencies of Signal and because it makes a lot of code that is unused.
I added tests for most of the code of class org.smssecure.smssecure.util.Hex
I hope @BLeQuerrec that you will be interested by this PR.