Before fixing the Category Removal Bug (commit 58537281), the "Default" Category would be empty when removing a populated category.
So when there is only one Category left, and the user hides that one Category, `tabCount` would be <= 0, leading to an Exception:
```
_AssertionError ('package:flutter/src/material/tab_controller.dart': Failed assertion: line 116 pos 15: 'initialIndex >= 0 && (length == 0 || initialIndex < length)': is not true.)
```
Now there is a check (`tabCount <= 0`), that IF tabCount is ever <= 0, it would show `_bodyWithoutCategories`.
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
```
getMangaChapterDirectory() now accepts an optional mangaMainDirectory
to avoid calling getMangaMainDirectory() and thus getDirectory() twice in places where both methods are called successively.
Added a checkbox "ignoreFiltersOnSearch" to the library search, so when checked, the whole library will be searched, not just the filtered library (Downloaded, Unwatched/Unread, Started, Bookmarked)
+ added some comments
