PixelOrb v0.2, Mobile support, new GUI, Level Menu

Just have updated my free and open-source game PixelOrb and now it supports mobile. I've already published it on Google Play Market, so if you have an Android phone you can go check it out.

https://play.google.com/store/apps/details?id=org.godotengine.pixelorbitch

Basically the problem was an awful performance of AnimatedSprite3D and Sprite3D on mobile platforms. The issue is still open in Godot Engine's Github repository. The workaround was making orbs MeshInstance and writing a custom shader for it. 

Adding level menu also was a major change. Now any level can be loaded from the level menu. Also, the menu has new About page. 

GUI is completely changed as well. I was trying to optimize it for mobile platform.

There is a full changelog:

## [0.2] - 2020-10-14

This update generally makes game run on mobile platforms, adds menus and changes GUI.

### Added
- Level menu
- About menu
- Shader for orbs
- **Mobile support**
- Adaptive icon for mobile

### Changed
- Orbs are made using MeshInstance and a custom shader instead of AnimatedSprite3D. AnimatedSprite3D has a very bad performance on mobile (GODOT Engine issue \# 20855)
- New GUI, mobile optimized
- PuzzleGenerator.gd and fake_perspective() in Puzzle.gd changed to work with new orbs improvement
- Sound volume decreased
- **Fixed** level now stars from 1

### Removed
- Level counter (replaced with menu button)
- Titles in the end (replaced with about menu). After beating all the levels, game starts from level 1

You can find the source code on this project's github page:

https://github.com/alex-karev/PixelOrb