Add export to word

[MatejFrnka]

Ended up writing custom logic for markdown to word conversion. This is not ideal, but I prefer it over the following other options:

• Using pandoc: this requires installing the pandoc-binary, which would make the deployment more annoying
• Using third party library: I only found libraries with around ~50 github stars, I would rather use a more adopted library
• Converting on client instead of on server: There also aren't that many widely adopted libraries for md to docx. It also increases the size of the plugin making the loading slower.

Based on this, I ended up implementing a simple convertor using two estabilished libraries (one for parsing md, one for editing docx).

closes #72

[MatejFrnka]

Review after merging PR #142