Update spawn and remove plugins

[bernardomovai]

Update spawn and removal plugins. Both plugins now receive a string with the names of the models to spawn/remove. Relates to https://movai.atlassian.net/browse/RP-1727 and https://movai.atlassian.net/browse/RP-1728

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[filipaexposto]

Looks good to me but would like to get @jmspribeiro opinion since it is more his area of expertise