Allow changing logo size in templates

[hql287]

Description

After trying out a few logos with different shapes and sizes, I realized that the current style/CSS doesn't work well in some cases, such as when the logo is very wide and short, or the opposite, very narrow and tall.

This PR fixed this issue by allowing the user to customize the logo size.

Related Issue

• Issue #160
• Issue #266

Motivation and Context

Increase flexibility in customizing templates.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.
• [ ] I have included a migration scheme (If type of change is breaking change)

[hql287]

@huyphams: This should fix #160 :)