use parcel to copy and rewrite references to static files

[tripodsan]

currently, we use our own heuristic to copy static files referenced in the HT(M)L.
with adobe/parcel-plugin-htl#16 solved, we can use the new parcel plugin to do so.

[tripodsan]

the new plugin processes the referenced files and cli moves the to dist:

$ hlx build
✨  Built in 1.05s.

.hlx/build/bootstrap.min.ef87a570.css    117.91 KB     28ms
.hlx/build/html.js                         8.58 KB    890ms
.hlx/build/lustig_html.js                  8.25 KB    915ms
.hlx/build/txt.js                          8.23 KB    953ms
.hlx/build/dump_html.js                    7.49 KB    982ms
├── src/dump_html.pre.js                   4.24 KB     16ms
└── src/dump_html.htl                      3.19 KB    923ms

.hlx/build/scripts.537edc24.js             3.23 KB     28ms
.hlx/build/favicon.64238bb4.ico            2.57 KB     35ms
.hlx/build/dump_html.map                   1.76 KB      3ms
(fix static .hlx/dist/favicon.64238bb4.ico)
(fix static .hlx/dist/bootstrap.min.ef87a570.css)
(fix static .hlx/dist/scripts.537edc24.js)

$ tree .hlx/build/ .hlx/dist/
.hlx/build/
├── dump_html.js
├── dump_html.map
├── html.js
├── lustig_html.js
└── txt.js
.hlx/dist/
├── bootstrap.min.ef87a570.css
├── favicon.64238bb4.ico
└── scripts.537edc24.js