closes#2393
this ammends my obviously incomplete fix in PR #2311.
This is just an UI issue. Subtitle track selection works, it just shows "No Captions" unfortunately.
* 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
* use Java I/O (classic way) on older android versions
* use Storage Access Framework on newer android versions (Android Lollipop or later)
* both changes have the external SD Card write permission
* add option to ask the save path on each download
* warn the user if the save paths are not defined, this only happens on the first NewPipe run (Android Lollipop or later)
* implement socket timeout error
* use 128k buffer size for copy
* use NewPipe HTTP user agent in the downloads
* automatically recover downloads with network errors that are queued
* replace "In queue" to "Pending" in the downloads header to avoid confusions (all languages)
* use 29bits Clusters size to support huge video resolutions (fixes#2291) (WebmWriter.java)
* add missing changes to WebmMuxer.java (i forget select the audio track)
* full support for Directory API (Android Lollipop or later)
* best effort to handle any kind errors (missing file, revoked permissions, etc) and recover the download
* implemented directory choosing
* fix download database version upgrading
* misc. cleanup
* do not release permission on the old save path (if the user change the download directory) under SAF api
* re-work finished mission database
* re-work DownloadMission and bump it Serializable version
* keep the classic Java IO API
* SAF Tree API support on Android Lollipop or higher
* add wrapper for SAF stream opening
* implement Closeable in SharpStream to replace the dispose() method
* do required changes for this API:
** remove any file creation logic from DownloadInitializer
** make PostProcessing Serializable and reduce the number of iterations
** update all strings.xml files
** storage helpers: StoredDirectoryHelper & StoredFileHelper
** best effort to handle any kind of SAF errors/exceptions
