Handle sender double spending transaction

Add transaction flag conflictingTxHash

Fix checkpoint block timestamp for bitcoin api sync.

Merge pull request #394 from horizontalsystems/add_migration

Add migration for change wrong checkpoint block timestamp

Swift 5. Dash LLMQ. Full sync optimizations

Use Swift 5

• Respectively use GRDB 4, RxSwift 5, etc

Add LLMQ support to Dash

• Full support of instant transactions
• Support protocol version >= 70214

Full sync optimizations

• Peer selection optimizations
• Ability to define sync mode:
  ** API (historical transactions from API, sync from peers network starting from last checkpoint)
  ** Full sync (starting from bip44 approval)
  ** New wallet (from last checkpoint)

Use P2WPKH(SH) address for receive by default

Make Kit extendible. Use GRDB. Dash support

Separate project to sub projects:

• BitcoinCore is the core project
• BitcoinKit uses BitcoinCore, only for Bitcoin blockchain
• BitcoinCashKit uses BitcoinCore, only for Bitcoin Cash blockchain
• DashKit uses BitcoinCore, only for Dash blockchain

Switch from Realm to GRDB

• Extract DB usages to single Interface
• Switch to GRDB storage

Dash support

• Handle Instant transactions
• Send AutoInstant transactions if possible

Lots of refactoring, optimizations and bugfixes

FeeRate sync bugfix

• fix bug with syncing issue for FeeRate (#264)

Improve Restore Performance

Customizable thread for delegate

Listener events are run in a dedicated background thread. It can be switched to main thread by setting the delegateQueue property to DispatchQueue.main.

Performance improvements

• improve threading and transfer heavy tasks to background thread (#237, #244, #245)
• restore performance improvement (#248, #254)
• "Double spend risk" on sent transactions is fixed (#247)
• bug fixes and improvements (#169, #221, #243, #249, #251, #258)

API and security improvements

• transactions list can now be fetched using Rx Single and accepts fromHash and limit parameters (#234)
• newWallet flag added to BitcoinKit constructor to avoid syncing from API for new wallet (#229)
• walletId has been added to constructor and used for DB name for security reasons (#217)
• proof of work verification has been fixed (#224)
• minor bug fixes and performance improvements (#209, #215, #218, #225)