Add initial project files and clean-up script

- Created a PowerShell script `clean.ps1` to remove build artifacts and temporary files.
- Added default instance configurations for "Default" and "Legacy Evolved" in JSON format.
- Introduced a guide in JSONC format detailing instance setup and configuration.
- Added an About dialog UI in XML format for the application.
- Included a license string for the GNU General Public License v3 in `license_str.py`.

data/defaults_instances/default.lce_inst

@@ -0,0 +1,11 @@
+{
+    "name": "Default",
+    "installation_path": ".lce", 
+    "username": "Steve", 
+    "archive_file": "LCEWindows64.zip", 
+    "exe_name": "Minecraft.Client.exe", 
+    "repo_url": "https://github.com/MCLCE/MinecraftConsoles", 
+    "instance_source": "InstanceSource.GITHUB_RELEASE", 
+    "instance_type": "InstanceType.CLIENT_VANILLA", 
+    "version": "nightly"
+}

data/defaults_instances/legacy_evolved.lce_inst

@@ -0,0 +1,11 @@
+{
+    "name" : "Legacy Evolved",
+    "installation_path": ".lce-evolved", 
+    "username" : "Steve",
+    "exe_name" : "Minecraft.Client.exe",
+    "archive_name" : "LCEWindows64.zip",
+    "url" : "https://codeberg.org/piebot/LegacyEvolved",
+    "instance_source": "InstanceSource.FORGEJO_RELEASE", 
+    "instance_type": "InstanceType.CLIENT_MODDED", 
+    "version" : "nightly" 
+}