Filter by severity value in the status tool

[lunkwill42]

Is your feature request related to a problem? Please describe.

Alert severity values were revamped for NAV 5.2. While there already exists a mechanism for making use of them in users' alert profiles, the status tool has no filter options for severity.

Describe the solution you'd like

The status tool filter controls should gain a widget for filter by severity level.

At minimum, it should allow for filtering all alerts above or below a certain threshold. Ideally, it should be able to let the user select which specific severity levels to include in the list.

The filtering is offloaded to the alert API call, in fact, so the API call needs to add this ability first.