Build: use a DOM-aware library to manipulate SVGs

Following from the discussion in #122, would be better if we were able to replace direct string manipulation with XML (SVG) aware libraries, such as [cheerio](https://github.com/cheeriojs/cheerio). This would make the code more reliable in the long term.

Example of direct string manipulation:

```
fileContent = fileContent.slice( 0, -6 ) +
'' +
fileContent.slice( -6 );
```

Start with the discussion in issue #122 and inspect the build code containing the shown direct string manipulation of SVG content. Compare the current approach with a DOM-aware library such as Cheerio and establish the reliability and completion criteria before attempting the broader refactor.

Written by the indexing model from the issue text.