Reverting usage of RE2 (WIP):

**Breaking changes**

The livechat v13 introduced a new library to handle regular expressions in forbidden words, to avoid
[ReDOS](https://en.wikipedia.org/wiki/ReDoS) attacks.
Unfortunately, this library was not able to install itself properly on some systems, and some admins were not able
to install the livechat plugin.

That's why we have disabled this library in v14, and introduce a new settings to enable regexp in forbidden words.
By default this settings is disabled, and your users won't be able to use regexp in their forbidden words.

The risk by enabling this feature is that a malicious user could cause a denial of service for the chat bot, by using a
special crafted regular expression in their channel options, and sending a special crafter message in one of their
rooms. If you trust your users (those who have rights to livestream), you can enable the settings. Otherwise it is not
recommanded. See the documentation for more informations.

**Minor changes and fixes**

* Channel's forbidden words: new "enable" column.
* New settings to enable regular expressions for channel forbidden words.
* "Channel advanced configuration" settings: removing the "experimental feature" label.

languages/cs.yml

@@ -488,7 +488,7 @@ prosody_firewall_configuration: Konfigurace mod_firewall Prosody
 prosody_firewall_disabled_warning: "Varování: mod_firewall je zakázán v nastavení
   <a href=\"/admin/plugins/show/peertube-plugin-livechat\" target=\"_blank\">pluginu</a>,
   pokud chcete, aby byla tato konfigurace zohledněna, musíte ji povolit.\n"
-prosody_firewall_file_enabled: Povoleno
+enabled: Povoleno
 prosody_firewall_name: Název
 prosody_firewall_name_desc: "Může obsahovat pouze: alfanumerické znaky, podtržítka
   a pomlčky.\nSkripty se načítají v abecedním pořadí.\n"