externalprovider: use temp table for query

This commit introduces a temporary table to KeychainExternal provider.
This is used to return a result set that contains the exact query as
identifying column, rather than the matching user id. This is helpful
because we match case insensitively internally, while the querying
implementation might wish to map search results against verbatim search
strings.

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/provider/KeychainExternalContract.java

@@ -38,6 +38,7 @@ public class KeychainExternalContract {
     public static class EmailStatus implements BaseColumns {
         public static final String EMAIL_ADDRESS = "email_address";
         public static final String EMAIL_STATUS = "email_status";
+        public static final String USER_ID = "user_id";
 
         public static final Uri CONTENT_URI = BASE_CONTENT_URI_EXTERNAL.buildUpon()
                 .appendPath(BASE_EMAIL_STATUS).build();