Add 12-character game link support

[jas14]

Closes #2291. This should do the trick for Android, but we will need to update apple-app-site-associations on lila for iOS.

I tested on an Android emulator using the following command:

adb shell am start -W -a android.intent.action.VIEW -d "https://lichess.org/2360tJXP000z#50" org.lichess.mobileapp

and substituted various URIs, including:

• https://lichess.org/2360tJXP000Z#50 (White's perspective at ply 50)
• https://lichess.org/2360tJXP000Z (White's perspective, no ply)
• https://lichess.org/2360tJXP000z (Black's perspective, no ply)

and some of the other link variations with just 8-character game IDs.

[veloce]

I guess I should merge it when the apple-app-site-association is updated on Lila.