Check_MK Werk 1482: Fix exception when editing a visual of type single host group

ID: 1482 Title: Fix exception when editing a visual of type single host group Component: Multisite Level: 1 Class: Bug Fix Version: 1.2.5i7 Context editor was broken, because there were two filters with the same HTML variable name <tt>hostgroup</tt>. This has been fixed by renaming the name of the host group selection filter to <tt>host_group</tt>.