Code snippets to download datasets with R, Python and curl

[arteymix]

• [x] add an action in the bottom toolbar to download using your favourite language/tool alongside download as TSV
• [ ] use a dialog component to propose snippets
• [x] use a tab component navigate between different tools/languages
• [x] add a copy button to copy the visible snippet
• [x] use a library to render the code neatly (i.e. highlight.js)

[arteymix]

Fully implemented and targeted for 0.4.3.