Refactor video access route

- Move errors to separate files instead of embedding
- Consistent interface for error generation
- Move renderVideo function into route
- Fix unhandled FetchError regression from dbbe950

pug/errors/fetch-error.pug

@@ -0,0 +1,5 @@
+p The selected instance, #[code= instanceOrigin], was unreachable.
+details
+  summary If the instance is on a private network
+  p The instance URL was resolved by the server. If the instance is on a private network, CloudTube will not be able to connect back to it.
+  p To get around this error, you may be able to use local mode, or you can run your own CloudTube within the network.

pug/errors/instance-error.pug

@@ -0,0 +1,4 @@
+p #[strong= error.message]
+if error.identifier
+  p #[code= error.identifier]
+p That error was generated by #[code= instanceOrigin].

pug/errors/message-error.pug

@@ -0,0 +1 @@
+pre= error.toString()

pug/errors/rate-limited.pug

@@ -0,0 +1,25 @@
+.blocked-explanation
+  img(src="/static/images/instance-blocked.svg" width=552 height=96)
+  .rows
+    .row
+      h3.actor You
+      | Working
+    .row
+      h3.actor CloudTube
+      | Working
+    .row
+      h3.actor Instance
+      | Blocked by YouTube
+    .row
+      h3.actor YouTube
+      | Working
+p.
+  CloudTube needs a working NewLeaf/Invidious instance in order to get data about videos.
+  However, the selected instance, #[code= instanceOrigin], has been temporarily blocked by YouTube.
+p.
+  You will be able to watch this video if you select a working instance in settings.
+  #[br]#[a(href="/settings") Go to settings →]
+p.
+  (Tip: Try #[code https://invidious.snopyta.org] or #[code https://invidious.site].)
+p.
+  This situation #[em will] be improved in the future!

pug/errors/unrecognised-error.pug

@@ -0,0 +1 @@
+pre= error.stack || error.toString()