Hide merged and obsolete series by default

[bonzini]

The idea is similar to how GMail hides "spam" and "trash" labels by default.

• If there are results, the series list view will show a checkbox at the bottom right corner, "Hide merged and obsoleted series", unless the search topic includes any of "is:merged" or "is:obsolete". The checkbox is checked by default and, if it is checked, the search query automatically does "-is:merged -is:obsolete".
• If there are no results, and again the search topic does not include either "is:merged" or "is:obsolete", the series list view will prompt "Do you want to include merged and obsolete series?" and add the appropriate GET parameter to the page.