Some Handlebars strings contained whitespaces characters at their ends.
With this, such characters are removed, as well as multiple spaces
(like the ones produced by code indentation).
This also includes a couple of fixes that removes spaces that were
intentionally placed before/after the string to translate.
Adds a new webhook integration for Slack to receive messages
from one's Slack team's public channels.
Contains negative tests for broken, missing or invalid data.
Allows two different option for integration:
1. Receive notification on a single stream with different topics
for each of Slack's public channels.
2. Receive notification on different streams for each of Slack's
public channels.
Steps to choose between the two options is described in the documentation.
Fixes#3569.
