Updated ws content sent on error

[zAlweNy26]

Description

As discussed in the past with @pieroit, I updated the content to send to the frontend when an error shows up, and also added the possibility to send an error via ws within a plugin.
I also fixed #434 as it was just 2 lines of code.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas