Prerelease with bug fixes and a new dedicate thumbnail widget feature.

## What's Changed
* Feature/audio player improvements by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/165
* Share option for widget content. by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/169
* Implements learning bar widget. by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/170
* Fixes group navigation bug. by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/173
* Adds file type check to audio player. by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/174
* Fixes persistent thumbnail issue after image widget is deleted. by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/175
* Fix widget title editing by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/176
* Fix: Suppress confirmation dialog on tag group autofill by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/177
* Fix: Properly clear piece thumbnail when source media is deleted by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/178
* Feat: Add dedicated Thumbnail widget by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/179
* Fix: Enable clearing thumbnailPath in MusicPiece.copyWith by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/180
* Fix: Implement Thumbnail widget functionality and separate rendering by @Adithya-Jayan in https://github.com/Adithya-Jayan/MyRepertoirApp/pull/181


**Full Changelog**: https://github.com/Adithya-Jayan/MyRepertoirApp/compare/v4.2.0+18...v4.3.0-prerelease.1+19
