Prepare iOS v1.6

[dpad85]

This pull request merges many fixes from master (that were cherry-picked in branch v1.6.x) into ios-hotfix, and prepare the release to mainnet. Note that this version depends on lightning-kmp 1.4.3.

This includes:

• update to Kotlin 1.6 with new memory model
• support for Tor
• various UI fixes and improvements for iOS
• a screen to close the wallet
• support for LNURL fallback scheme
• a simple CSV export
• improved handling of iOS notification permissions