Add font highlighting for `ArticleView`

[aome510]

Brief description of changes

• implement a parser (font highlighting) for parsing article's content (in HTML) into styled text
• add left-right paddings for ArticleView
• label link IDs in ArticleView to start with 1
• move Article struct from view module to client module
• upgrade dependencies, replace htmlescape with html-escape
• add html5ever and markup5ever_rcdom for parsing HTML document
• rename functions/variables, simplify comment parsing function
• add header, bold component styles

Breaking changes

• require the article's content received from article_parse_command to be in HTML format
• change the default article_parse_command to mercury-parser without additional arguments
• remove toggle_raw_markdown_mode command