Text layer recognition

#176 and #178 really depend on resources having text layer attached when possible.

We can extract text relatively easily from:
* content of text-based resources
* metadata of some file types (JPG, MP3)

We can extract text with some effort from:
* images (e.g. screenshots of web pages, or photos with shop labels)
* audio (useful for voice-notes, which possible to make while driving a car)

Text layers should be stored in hidden folder, alongside with tags storage and index, and should be managed by [arklib](https://github.com/ARK-Builders/arklib/).

Start by reviewing issues #176 and #178, then inspect how Navigator currently stores tags and its index. Investigate arklib's resource-management capabilities and determine how text from text resources, metadata, images, and audio can be attached in a hidden folder alongside those stores; done means the text layers are managed by arklib and available when extraction is possible.

Written by the indexing model from the issue text.