#21: Add show content above

[EddieLukeAtmey]

Please review and merge.

Change:

• Add new property.
• Adjust scrollView content offset when presenting and dismiss.
• If not scrollView && isShowAbove, keep original size instead of crop content's height.

Future implement:

• Make auto calculation to show content above or below.

[maxkonovalov]

Hi @EddieLukeAtmey! This is a great addition, I tried it out and it worked like a charm 👍

I'd like to add a couple things, so I'll merge this PR to a separate branch first.

[maxkonovalov]

I updated the disclosure indicators to be flipped by default when the content is shown above: 6631486f3860daa4ab72548bad84a54bd99a5356

[maxkonovalov]

There is also an issue with dismissing the dropdown when it's showing above – it gets dismissed when tapping anywhere outside the dropdown.

The expected behaviour should be the same as for the default presentation:

1. When tapped above the menu and outside the presented dropdown, it should be dismissed.
2. When tapped on the menu components, it should dismiss the presented dropdown and then present another for the selected component (if it is different).
3. When tapped below the menu, no action should be made, i.e. do not dismiss the presented dropdown.

@EddieLukeAtmey can you please review the above and try to fix it in your branch

[maxkonovalov]

Also, this issue can be noticed when setting a non-zero dimming opacity: cell.dropdownMenu.backgroundDimmingOpacity = 0.25;