i18n-pl: Provide translations for plural forms of reservations. emails, messages

Following up on the previous commit this one introduces Polish
translations for plural forms of reservations. emails, messages in
upgrade modal.

web/public/static/langs/pl.json

@@ -308,5 +308,14 @@
     "account_upgrade_dialog_button_pay_now": "Zapłać i aktywuj subskrypcję",
     "account_tokens_dialog_button_cancel": "Anuluj",
     "account_tokens_dialog_expires_label": "Token dostępowy wygasa po",
-    "account_tokens_dialog_expires_unchanged": "Pozostaw termin ważności bez zmian"
+    "account_tokens_dialog_expires_unchanged": "Pozostaw termin ważności bez zmian",
+    "account_upgrade_dialog_tier_features_reservations_one": "{{reservations}} rezerwacja tematu",
+    "account_upgrade_dialog_tier_features_reservations_few": "{{reservations}} rezerwacje tematów",
+    "account_upgrade_dialog_tier_features_reservations_many": "{{reservations}} rezerwacji tematów",
+    "account_upgrade_dialog_tier_features_emails_one": "{{emails}} mail dziennie",
+    "account_upgrade_dialog_tier_features_emails_few": "{{emails}} maile dziennie",
+    "account_upgrade_dialog_tier_features_emails_many": "{{emails}} maili dziennie",
+    "account_upgrade_dialog_tier_features_messages_one": "{{messages}} wiadomość dziennie",
+    "account_upgrade_dialog_tier_features_messages_few": "{{messages}} wiadomości dziennie",
+    "account_upgrade_dialog_tier_features_messages_many": "{{messages}} wiadomości dziennie"
 }