Improve issue templates

The bug report template was inspired by Godot's.

Using an empty template is no longer allowed to increase the likelihood
that people fill in the required fields when reporting bugs.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -7,4 +7,21 @@ assignees: ''
 
 ---
 
-*Please specify your ArmorPaint version and OS.*
+<!-- Please search existing issues for potential duplicates before filing yours:
+https://github.com/armory3d/armorpaint/issues?q=is%3Aissue
+-->
+
+**ArmorPaint version:**
+<!-- Specify commit hash if using non-official build. -->
+
+
+**OS/device including version:**
+<!-- Specify GPU model, drivers, and the backend (non-DXR or DXR) if graphics-related. -->
+
+
+**Issue description:**
+<!-- What happened, and what was expected. -->
+
+
+**Steps to reproduce:**
+<!-- If needed, include screenshots by drag and dropping them. -->