Convert HTML tags in issues from rich text editor to Slack markdown

[alterdaemon]

On Description or Note updates there are html tags in the message.

e.g. ew <br d<br /

<'img alt="" data-rich-file-id="135" src="/redmine/system/rich/rich_files/rich_files/000/000/135/thumb/screen-20shot-202015-01-21-20at-2014-34-53.png" />

the plugin would use an option to strip all the html tags for a clean text

[berdyshev]

Voting, because now such notifications look weird and not readable.