Ability to hide features that extend beyond a specified window

[ilevantis]

Would be incredibly helpful (especially with RNASeq / RNASeq Coverage) to hide all features in any(all) tracks that lie outside a specified window.

1. This would be an easy way to get rid of mis-mapped RNASeq reads which have skips that are extremely long and span between genes.
2. It would remove the visual clutter of other features that are obviously too long (therefore likely irrelevant) for what is being investigated.
3. I imagine this could potentially improve performance when only investigating a small region.