#20 Bdkrm fix tag groups with multiple words in name

#20 [bdrkm] Use better display for groups and tags in groups

#19 better display for Bootstrap darkroom

#18 bad performances with many tag groups
#10 use same style as mainline tags page (for nb_entries)

PHP 8 compatibility

New languages:
* Icelandic (Íslenska [IS])

Dynamic filters: if you use the multi-criteria search with groups of tags, you can now only display the "not disabled" tags for combination. Use the following setting in LocalFiles Editor:

$conf['tag_groups_index_filters'] = true;
$conf['tag_groups_dynamic_filters'] = true;

#13 specific id for each filter (simpler to customize)

#4 Use groups as filters on thumbnails page

To use this nice new feature, add in your local configuration:

$conf['tag_groups_index_filters'] = true;

New languages:
* Bulgarian (Български [BG])
* Catalan (Català [CA])
* Czech (Česky [CZ])
* Danish (Dansk [DK])
* German (Deutsch [DE])
* Greek (Ελληνικά [GR])
* Esperanto (Esperanto [EO])
* Spanish (Español [ES])
* Finnish (Finnish [FI])
* Hungarian (Magyar [HU])
* Italian (Italiano [IT])
* Japanese (日本語 [JP])
* Cambodia (ខ្មែរ [KH])
* Latvian (Latviešu [LV])
* Norwegian (Norsk bokmål [NO])
* Dutch (Nederlands [NL])
* Polish (Polski [PL])
* Portuguese Brazil (Brasil [BR])
* Portuguese (Português [PT])
* Romanian (Română [RO])
* Russian (Русский [RU])
* Slovak (Slovensky [SK])
* Slovenian (Slovenščina [SL])
* Serbian (Српски [SR])
* Swedish (Svenska [SE])
* Thai (ภาษาไทย [TH])
* Turkish (Türkçe [TR])
* Ukrainian (Українська [UA])
* Vietnamese (Việt [VN])
* Chinese (中文 (简体) [CN])
* Traditional Chinese (中文 (繁體) [TW])

First version.

Create tags country:USA, country:France, weather:sunny, weather:cloudy. Then you have 2 groups country and weather.