Models and Schemas panel style and accessibility improvements

[tkajtoch]

Acceptance Criteria

• Header: panel title should be wrapped in h4 tag instead of h1 tag
• Header: the arrow icon should be placed on the left side (instead of being to the right of the title; keep it inside the title h4 tag)
• Header: the spacing between arrow and title text should have 1rem
• Header: there should be a border-bottom and cursor: pointer set on the whole heading
• Model / Schema container should have a configurable background via --model-container-background CSS variable and fallback to #ededed if not set
• Model / Schema container should be spaced 1.25rem from each other
• Model / Schema should have a configurable color and font properties via --model-title-color (fallback to #333333), --model-title-font-size (fallback to 1rem), --model-title-font-weight (fallback to 600) CSS variables
• Model / Schema arrow right icon should be centered vertically, and its fill color should be configurable via --model-collapse-icon-color (fallback to #07A88D) CSS variable
• Model / Schema object opening brace (.brace-open .model and .brace-open .object) should have display: block; and margin-top: 0.5rem
• Model / Schema object table renderedMarkdown class should override default markdown font sizes to 0.75rem
• Model / Schema object prop-type should have a configurable color via --model-prop-type-color (fallback to #07A88D)

[pk-hotovo]

Implemented

[tomaszwylezek]

Closing in favor of #94