This commit moves the import of viz.js into a `require.ensure` block,
that is only executed when a graphviz diagram is actually present
in a note. Webpack automatically splits the library into a separate
chunk and loads that on demand.
To ensure that graphviz code-blocks are not treated as normal
code-blocks while the chunk is loading, a corresponding check is added
to `finishView`.
The library is also removed from the Webpack config file, as it only
is used at one place in extra.js, which is handled by Webpack
without any extra config.
Signed-off-by: David Mehren <git@herrmehren.de>
5b8b76135b