feat: manage extensions navbar (#2121)

* feat: manage extensions navbar
create now `Manage` spacer in sidebar. and add manage extensions to it
closes #2088
* do not show when no exts
* update cn and jp i18n strings
* rename lnbits-admin-ui component to lnbits-manage, fix its behaviour
* i18n: add Korean language

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Co-authored-by: Pavol Rusnak <pavol@rusnak.io>
Co-authored-by: psychoet <125599543+psychoet@users.noreply.github.com>

package.json

@@ -80,6 +80,7 @@
       "i18n/br.js",
       "i18n/cs.js",
       "i18n/sk.js",
+      "i18n/kr.js",
       "js/base.js",
       "js/components.js",
       "js/components/lnbits-funding-sources.js",