Users can now add Mangas/Animes to a **manually** created Mangayomi/local folder.
Feature as described:
```
App Home Location/
local/
Manga Title/
cover.jpg (optional)
Chapter 1/
1.jpg
...
Chapter 2.cbz
...
Anime Title/
cover.png (optional)
Episode 1.mp4
Episode 2.mkv
```
The folder (if exist) will be scanned once per app start.
**Supported filetypes:** (taken from lib/modules/library/providers/local_archive.dart, line 98)
```
Videotypes: mp4, mov, avi, flv, wmv, mpeg, mkv
Imagetypes: jpg, jpeg, png, webp
Archivetypes: cbz, zip, cbt, tar
```
- Instead of manually concatenating filepathes, it's using the path.join() function now.
- switched some if conditions, that had nothing in the if block, but in the else block, removing the redundant else block.
