added renderFooter in DrawerNavigation

[nehvaleem]

As mentioned in #330 I've added a renderFooter to DrawerNavigation. In my project it was necessary so I've thought that maybe someone will find it useful.

[chirag04]

related:https://github.com/exponent/ex-navigation/pull/182

[zoontek]

renderFooter can be way easier to use than implementing his own Drawer navigation view using renderNavigationView 👍 (if you only need a drawer footer)

[zoontek]

Any ETA on this?

[nehvaleem]

@zoontek i don't know why i missed your comment. Correct me if i am wrong, but adding footer in renderNavigationView would need some additional styling to make footer fixed at bottom of the screen instead of adding it after current items. I would rather avoid that for simplicity sake. You could also add header the way u described, but it is moved to separate method :)

edit: yeah, instead of simply adding footer you have to write again how to render items, handle item selection etc. Imo the way I suggested is easier.