Minor 1.5 (#18)

- Updated repository documentation: added contribution guidelines, Code of Conduct, GitHub templates
- Updated README
- Added confirmation dialog for tabs and collections deletion (#17)
- Complete code refactoring (HTML/JS/CSS)
- Implemented <iframe> base for embedded pane (#13) (Fixed CSS instability on some websites)
- Improved dark theme
- Added opensource fonts to replace Segoe UI on Unix systems (#11, #17)
- Fixed invisible vertical scrollbar
- Code polish and improvement

Co-authored-by: Amine A. <15179425+AmineI@users.noreply.github.com>
Co-Authored-By: Michael Gordeev <michael@xfox111.net>

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,20 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: enhancement
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when '...'
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.