Add machine select-box to alerts

[ADANBacki]

Adds a select box to the alerts page, where a machine can be selected from the case. The alerts then displayed refer only to the selected machine. There is also an option to evaluate them for "all machines" with the behavior as before. The select box is searchable, the machines are alphabetically sorted.
The default route to the alert page now initially shows nothing until something is selected via the selection box. The reason for this is performance problems when many rules and machines are present in a case and all rules would be evaluated by default.