shrink bytecode with ProGuard for both debug/release builds (closes #202)

* enable ProGuard for debug builds because real-life testing is done with debug builds

app/build.gradle

@@ -11,10 +11,13 @@ android {
     }
 
     buildTypes {
+        debug {
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
+        }
         release {
-            minifyEnabled false
-            // minifyEnabled true
-            // proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
         }
     }
     dexOptions {
@@ -32,7 +35,7 @@ dependencies {
     compile 'org.apache.commons:commons-io:1.3.2'
 
     // Lombok for useful @helpers
-    compile 'org.projectlombok:lombok:1.14.8'
+    provided 'org.projectlombok:lombok:1.14.8'
 
     // ical4j for parsing/generating iCalendars
     compile 'org.mnode.ical4j:ical4j:1.0.6'

app/proguard-rules.txt

@@ -0,0 +1,33 @@
+
+# ProGuard usage for DAVdroid:
+# 	shrinking		yes - main reason for using ProGuard
+# 	optimization		no - too risky
+# 	obfuscation		no - DAVdroid is open-source
+# 	preverification		no (Android default)
+
+-dontobfuscate
+
+
+# SimpleXML
+-keep class org.simpleframework.** { *; }	# keep all interfaces etc. to allow reflection
+-dontwarn com.bea.xml.stream.**			# StAX API not used
+-dontwarn javax.xml.stream.**
+
+# ez-vcard
+-dontwarn com.fasterxml.jackson.**		# Jackson JSON Processor (for jCards) not used
+-dontwarn freemarker.**				# freemarker templating library (for creating hCards) not used
+-dontwarn org.jsoup.**				# jsoup library (for hCard parsing) not used
+-dontwarn sun.misc.Perf
+
+# ical4j: ignore unused dynamic libraries
+-dontwarn groovy.**				# Groovy-based ContentBuilder not used
+-dontwarn org.codehaus.groovy.**
+-dontwarn org.apache.commons.logging.**		# Commons logging is not available
+-dontwarn net.fortuna.ical4j.model.**		# ignore warnings from Groovy dependency
+
+# dnsjava
+-dontwarn sun.net.spi.nameservice.**		# not available on Android
+
+# DAVdroid
+-keep class at.bitfire.davdroid.** { *; }	# all DAVdroid code is required
+