explorer: Allow passing seed and base as arguments

Also take a default value from configuration.

Fix all usages and change some hardcoded links to use the filter.

_plugins/explorer.rb

@@ -1,12 +1,15 @@
 module Jekyll
   module Explorer
-    def explore(input)
-      base = "https://radicle.network/nodes"
-      if input.include?(' ')
-        prefix, suffix = input.split(' ', 2)
-        "#{base}/#{prefix}/#{suffix}"
+    def explore(
+      input,
+      node = @context.registers[:site].config['node'],
+      explorer = @context.registers[:site].config['explorer']
+    )
+      base = "https://#{explorer}"
+      if input.nil?
+        base
       else
-        "#{base}/iris.radicle.xyz/#{input}"
+        "#{base}/nodes/#{node}/#{input}"
       end
     end
   end