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/app/src/main/res/xml/settings.xml

@@ -13,12 +13,6 @@
         android:key="jc_settings"
         >
 
-        <SwitchPreference
-            android:title="@string/applet_helloworld"
-            android:switchTextOn="@string/aid_helloworld"
-            android:key="activate_helloworld"
-            android:defaultValue="false"
-            />
         <SwitchPreference
             android:title="@string/applet_openpgp"
             android:switchTextOn="@string/aid_openpgp"
@@ -100,7 +94,7 @@
 
         <Preference
             android:title="Emulation with Gear's NFC"
-            android:summary="Samsung Gear needs to be installed for using the Gear's NFC emulation capabilities."
+            android:summary="Samsung Gear needs to be installed for using the Gear's NFC emulation capabilities. (Disabled on F-Droid)"
             android:key="gear_nfc">
         </Preference>