[#2560] run entry excerpts through HTML cleaner instead of escaping everything

[kareila]

I took a wild stab at this - the options for the cleaner may need to be tweaked further, but this seems like a reasonable first attempt.

Fixes #2560.

[nfagerlund]

The way all these old BML pages call all these low-level functions constantly makes my skin crawl. 😖

So, LJ::Entry objects already have an event_html_summary method -- would it make more sense to just grab some item IDs ($u->recent_items? at least that's what S2 does), make entry objects, and call that?

The only problem I could think of would be performance concerns, but it seems like that shouldn't be any nastier than just building a last-N journal page, yeah? I checked to see how outrageous this list gets, and while the form will let you request up to 99, it seems to ignore that and actually cap it at 50.

[kareila]

I'm happy to investigate that alternative - I'll flag this as having requested changes until I have time to try it out.