ACardEmulator: Added F-Droid build flavor with FOSS only

- avoid precompiled JARs for JCardSim
- use gradle's shadow plugin to relocate JCardSim's use of Bouncycastle
- removes JCardSim's Hello world applet
- use vJCRE to avoid importing Oracle's api_classic.jar

(We may use vJCRE as full replacement for JCardSim in the future, but
JCardSim is currently the choice with more features and support)

ACardEmulator/build.gradle

@@ -6,6 +6,7 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:2.3.3'
+        classpath 'com.github.jengelman.gradle.plugins:shadow:2.0.4'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files