Better support for tap and longPress

Currently it's hard to use tap and long press events on the images.

I want to use in the same time:

• tap (fast press) to show/hide photo infos
• long press to select the photo

Long press delay is hardcoded to 600ms here: https://github.com/archriss/react-native-image-gallery/blob/master/src/Gallery.js#L133

onSingleTapConfirmed is more suited to ensure that it is a singleTap (vs a double tap) but is slow to fire and has a 500ms delay: https://github.com/ldn0x7dc/react-native-gesture-responder/blob/master/library/createResponder.js#L220

It would be nice to make these 2 delays configurable so that it's easy to detect a single press / long press. The most annoying is to have the delay on single press. Could we have something like onPress, similar to the longpress code, but with a much shorter default delay (like 150) and make both delays configurable?

Start in src/Gallery.js around the hardcoded 600ms long-press delay, then inspect onSingleTapConfirmed in react-native-gesture-responder's library/createResponder.js. Define how configurable single-press and long-press delays should interact, implement the requested defaults, and verify that tap and long-press image interactions can be distinguished.