Add more custom modes

[mhsattarian]

Some custom modes I created are added to the list in MODES.md file.
here is a preview:

• Snapping Mode: Add snapping ability while drawing features
• Pinning Mode: Pin shared coordinates together during edit
• Passing Mode: Add ability to draw features but don't add them
• Select Feature Mode: Select features by click and highlight on hover

[mhsattarian]

Sorry for making this PR pop up again, I just realized I'd forgotten to resolve changes suggested by @clementmas.

[mhsattarian]

I've added one more mode I created recently.
and can this be finally merged? this PR has been open for around 2 years!

[3zzy]

@mhsattarian Great work! Sad that its not been merged yet :(

[mhsattarian]

Thanks @3zzy, I don't know why either. it's taking so long that I don't work on GIS-related applications anymore!

I really like and respect the Mapbox team's work and effort. I don't know why such a useful project has such slow progress.

[stepankuzmin]

Thanks for the contribution, @mhsattarian!