New GUI: severity level filters do not work

[tgreenx]

This relates to the new GUI implementation (#511)
As the title states, the severity level filters of the result page do not seem to work at all on a latest installation of the new GUI (#511, commit ffc9eb3). Messages are not getting filtered.

[tgreenx]

@tbleckert Hi again, sorry, could you have a look at this? Recent changes seem to have impacted this functionality.

[tbleckert]

@tgreenx I'll take a look