Unify LuaSocket usage (#7405)

* Add a new socketutil module with a few helper functions that allow us to:
  * Always use a sane User-Agent (previously, only Wikipedia did so)
  * Set timeouts in an almost sane manner. Doing it explicitly prevents an interaction with KOSync that does crazy stuff I don't even want to try to understand.
* Unified said timeouts based on the request's intended usage (except for Wikipedia, which already had meaningful timeout values).
* Stopped using LuaSec directly, LuaSocket defers to LuaSec sanely on its own. Everything now transparently supports HTTPS without code duplication.

frontend/apps/reader/modules/readerdictionary.lua

@@ -965,25 +965,21 @@ end
 function ReaderDictionary:downloadDictionary(dict, download_location, continue)
     continue = continue or false
     local socket = require("socket")
+    local socketutil = require("socketutil")
     local http = socket.http
-    local https = require("ssl.https")
     local ltn12 = require("ltn12")
-    local url = socket.url
-
-    local parsed = url.parse(dict.url)
-    local httpRequest = parsed.scheme == "http" and http.request or https.request
 
     if not continue then
         local file_size
-        --local r, c, h = httpRequest {
-        local dummy, headers, dummy = socket.skip(1, httpRequest{
-            method = "HEAD",
-            url = dict.url,
+        -- Skip body & code args
+        socketutil:set_timeout()
+        local headers = socket.skip(2, http.request{
+            method  = "HEAD",
+            url     = dict.url,
             --redirect = true,
         })
-        --logger.dbg(status)
+        socketutil:reset_timeout()
         --logger.dbg(headers)
-        --logger.dbg(code)
         file_size = headers and headers["content-length"]
 
         UIManager:show(ConfirmBox:new{
@@ -1004,10 +1000,12 @@ function ReaderDictionary:downloadDictionary(dict, download_location, continue)
         end)
     end
 
-    local dummy, c, dummy = httpRequest{
-        url = dict.url,
-        sink = ltn12.sink.file(io.open(download_location, "w")),
-    }
+    socketutil:set_timeout(socketutil.FILE_BLOCK_TIMEOUT, socketutil.FILE_TOTAL_TIMEOUT)
+    local c = socket.skip(1, http.request{
+        url     = dict.url,
+        sink    = ltn12.sink.file(io.open(download_location, "w")),
+    })
+    socketutil:reset_timeout()
     if c == 200 then
         logger.dbg("file downloaded to", download_location)
     else