Better Extruder Idler Door for Bear Extruder

Improve design of extruder idler door for bear extruder to suit my needs.

1. Make window bigger so easier to see filament and bondtech gears.
2. Add notch to stick fingernail in to open door easier.
3. Reduce weight of extruder with less plastic.

This is for [bear extruder](https://www.thingiverse.com/thing:3226689) by Greg Saun. It's a much better extruder than stock Prusa MK3 extruder. This will not work on stock MK3 extruder.

**Change Log:**

1/19/2018
V2 - Made window even bigg