Add page down/page up hardware detection (#1212)

* Added page down and page up key event.  Have it always on since page down and page up buttons are only on readers or keyboards

* moved code to different method

* added spaces back to comments

app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderActivity.kt

@@ -218,6 +218,8 @@ class ReaderActivity : BaseRxActivity<ReaderPresenter>() {
                 KeyEvent.KEYCODE_DPAD_LEFT -> viewer?.moveLeft()
                 KeyEvent.KEYCODE_DPAD_DOWN -> viewer?.moveDown()
                 KeyEvent.KEYCODE_DPAD_UP -> viewer?.moveUp()
+                KeyEvent.KEYCODE_PAGE_DOWN -> viewer?.moveDown()
+                KeyEvent.KEYCODE_PAGE_UP -> viewer?.moveUp()
                 KeyEvent.KEYCODE_MENU -> toggleMenu()
                 else -> return super.onKeyUp(keyCode, event)
             }