Add line-height setting option to the heading component

• Add a new line_height property to the heading component.
• Add parentheses around pixel font sizes for to make options more understandable in font size property.
• Fix typo in font size property (pixel sizes of 8xl and 7xl were mixed).
• Remove line height settings from heading-tailwind.css because they overrode the settings in the properties.
• Add the line height to the heading template.