79603688¬ grid view performance improvement

@lefticus please review these proposed changes; although I tested the changes, I need a sanity check.
@evanweaver I'd prefer if you used `QSignalBlocker` (http://qt-project.org/doc/qt-5/qsignalblocker.html) instead, which is one call instead of two, and automatically unblocks signals when it goes out of scope, which would prevent any accidental unmatched block/unblock pair.

I probably have time to make the changes, if you've already moved on to other things.