Allow HTML tags in external markdown files

Use textContent instead of innerHTML to prevent encoding of certain characters in Markdown code blocks.

show error when notes run on non-http, fix load order to make sure upcoming slide is correct when notes open (#278)

update syntax highlight after editing (#210), move markdown and highlight scripts from lib to plugin

Its was impossible (at least for me) to keep the windows in sync without bloating the code too much.

See b957d0b8

Might be better to use one variable with different values.

And emit 'fragmentchanged' with the appropriate fragmentData to show or hide fragments.