Add log host_id index and use it first in history research filter 

On larger installations with a lot of log lines (I have now around 60 millions) the history search is really slow. In a full search this is acceptable and I increased the fcgi timeouts so that it is still displayed also if the query is taking > 3 minutes. But if I just search the entries for a host/service that this should be faster. With this change just adding the index I went down from 3 to 2 minutes, but with the small patch in the Controller I went down from 2 minutes to 0.09 minutes ;)