Space reserving tweaks for huge video resolutions

* improve space reserving, allows write better 4K/8K video data
* do not use cache dirs in the muxers, Android can force close NewPipe if the device is running out of storage. Is a aggressive cache cleaning >:/
* (for devs) webm & mkv are the same thing
* calculate the final file size inside of the mission, instead getting from the UI
* simplify ps algorithms constructors
* [missing old commit message] simplify the loading of pending downloads

app/src/main/java/us/shandian/giga/util/Utility.java

@@ -267,8 +267,7 @@ public class Utility {
         }
 
         try {
-            long length = Long.parseLong(connection.getHeaderField("Content-Length"));
-            if (length >= 0) return length;
+            return Long.parseLong(connection.getHeaderField("Content-Length"));
         } catch (Exception err) {
             // nothing to do
         }