Fix proguard rules for ezvcard and ical4j.

app/proguard-rules.txt

@@ -22,15 +22,17 @@
 -dontwarn ezvcard.io.json.**            # JSON serializer (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
--keep,includedescriptorclasses class ezvcard.property.** { *; }  # keep all VCard properties (created at runtime)
+-keep class ezvcard.property.** { *; }  # keep all vCard properties (created at runtime)
 
 # ical4j: ignore unused dynamic libraries
 -dontwarn aQute.**
 -dontwarn groovy.**                       # Groovy-based ContentBuilder not used
+-dontwarn javax.cache.**                  # no JCache support in Android
+-dontwarn net.fortuna.ical4j.model.**
 -dontwarn org.codehaus.groovy.**
--dontwarn net.fortuna.ical4j.model.**     # ignore warnings from Groovy dependency
--keep,includedescriptorclasses class net.fortuna.ical4j.** { *; }  # keep all model classes (properties/factories, created at runtime)
+-dontwarn org.apache.log4j.**             # ignore warnings from log4j dependency
+-keep class net.fortuna.ical4j.** { *; }  # keep all model classes (properties/factories, created at runtime)
+-keep class org.threeten.bp.** { *; }     # keep ThreeTen (for time zone processing)
 
 # okhttp
 # JSR 305 annotations are for embedding nullability information.