Enhancement/Reduce bundle size

[c-w]

This pull request reduces the webpack bundle size by:

• Splitting mixin.js into two modules so that the dependencies of each mixin only get included in the bundles of views that use the mixin and not in other bundles.
• Removing all unused highlight.js languages.
• Scoping the vue-chartjs imports.

The size savings resulting from these changes can be seen in the table below:

Before	After	Bundle
16K	16K	dataset
140K	140K	demo_named_entity
140K	140K	demo_text_classification
136K	136K	demo_translation
744K	176K	document_classification
728K	120K	download_seq2seq
728K	120K	download_sequence_labeling
728K	120K	download_text_classification
128K	128K	guideline
120K	120K	index
116K	116K	label
112K	112K	projects
740K	172K	seq2seq
744K	180K	sequence_labeling
520K	487K	stats
728K	120K	upload_seq2seq
728K	120K	upload_sequence_labeling
728K	120K	upload_text_classification

[jondavidjohn]

I built a tool to help you analyze webpack bundles for size regressions, and report them directly to GitHub PRs. It's free for open source, so it might be worth checking out and helpful to keep these optimizations from needing to happen again!

https://packtracker.io

[c-w]

Nice! Thanks for the pointer.

@Hironsan would you consider integrating @jondavidjohn's tool?