Accept 2 new props for DrawerItems (disabled, handlesDrawerToggle)

[cooperka]

New props:

• disabled: Passed though to TouchableWithoutFeedback, as well as to render functions such as renderTitle.

• handlesDrawerToggle: For items that will handle closing the drawer (or not) themselves after being pressed. If this prop is truthy, these items will not cause the drawer to close automatically.

Reason for adding:

I have "section headers" in my drawer that help visually group a few related items together. They shouldn't respond to touch events, and are thus disabled.

I also currently have a drawer item called "Check Updates" that simply shows a spinner while checking for updates. No route is pushed, and the drawer should not be closed.

Screenshot of my app using the new props:

Misc.

Also minorly updates the README with a relevant link to source for DrawerNavigationItem, and gitignores a directory that's auto-generated by IntelliJ.

Please let me know if there's any testing or linting you'd like me to do before merging this!
Thanks 🌵

[dantman]

I'm in favour of being able to disable items. However I don't think that headings should be implemented that way (they shouldn't be wrapped in a touchable area at all), non-navigation chunks should be supported explicitly #227.

[cooperka]

I agree @dantman, a more extensive change like you're proposing would make things like this a lot easier. I'd be interested in helping work on that once this is merged.