Fix issue with slash (/) characters in B2 Application Key

Urlencode B2 Application Key when saving configuration, urldecode it
back when reading. Duplicity accepts urlencoded target directly, no
decoding is necessary when backup is performed.

Resolve #1964

management/backup.py

@@ -509,7 +509,7 @@ def list_target_files(config):
 		
 		# Extract information from target
 		b2_application_keyid = target.netloc[:target.netloc.index(':')]
-		b2_application_key = target.netloc[target.netloc.index(':')+1:target.netloc.index('@')]
+		b2_application_key = urllib.parse.unquote(target.netloc[target.netloc.index(':')+1:target.netloc.index('@')])
 		b2_bucket = target.netloc[target.netloc.index('@')+1:]
 
 		try:

management/templates/system-backup.html

@@ -291,7 +291,7 @@ function show_custom_backup() {
           var b2_applicationkey = targetPath.split(':')[1].split('@')[0];
           var b2_bucket = targetPath.split('@')[1];
           $("#backup-target-b2-user").val(b2_application_keyid);
-          $("#backup-target-b2-pass").val(b2_applicationkey);
+          $("#backup-target-b2-pass").val(decodeURIComponent(b2_applicationkey));
           $("#backup-target-b2-bucket").val(b2_bucket);
         }
         toggle_form()
@@ -316,7 +316,7 @@ function set_custom_backup() {
                                                                 + "/" + $("#backup-target-rsync-path").val();
     target_user = '';
   } else if (target_type == "b2") {
-    target = 'b2://' + $('#backup-target-b2-user').val() + ':' + $('#backup-target-b2-pass').val()
+    target = 'b2://' + $('#backup-target-b2-user').val() + ':' + encodeURIComponent($('#backup-target-b2-pass').val())
         + '@' + $('#backup-target-b2-bucket').val()
     target_user = '';
     target_pass = '';