daemon: refactor load_wallet to not just return None, but raise specific exceptions.

The following exceptions should be expected:
FileNotFoundError: given wallet path does not exist
StorageReadWriteError: given file is not readable/writable or containing folder is not writable
InvalidPassword: wallet requires a password but no password or an invalid password was given
WalletFileException: any internal wallet data issue. specific subclasses can be caught separately:
-  WalletRequiresSplit: wallet needs splitting (split_data passed in Exception)
-  WalletRequiresUpgrade: wallet needs upgrade, and no upgrade=True was passed to load_wallet
-  WalletUnfinished: wallet file contains an action and needs additional information to finalize. (WalletDB passed in exception)

Removed qml/qewalletdb.py

This patch also fixes load_wallet calls in electrum/scripts and adds a qml workaround for dialogs opening and closing so
fast that the dialog opened==true property change is missed (which we need to manage the dialog/page stack)

electrum/gui/qml/qeapp.py

@@ -25,7 +25,6 @@ from .qedaemon import QEDaemon
 from .qenetwork import QENetwork
 from .qewallet import QEWallet
 from .qeqr import QEQRParser, QEQRImageProvider, QEQRImageProviderHelper
-from .qewalletdb import QEWalletDB
 from .qebitcoin import QEBitcoin
 from .qefx import QEFX
 from .qetxfinalizer import QETxFinalizer, QETxRbfFeeBumper, QETxCpfpFeeBumper, QETxCanceller
@@ -332,7 +331,6 @@ class ElectrumQmlApplication(QGuiApplication):
         ElectrumQmlApplication._daemon = daemon
 
         qmlRegisterType(QEWallet, 'org.electrum', 1, 0, 'Wallet')
-        qmlRegisterType(QEWalletDB, 'org.electrum', 1, 0, 'WalletDB')
         qmlRegisterType(QEBitcoin, 'org.electrum', 1, 0, 'Bitcoin')
         qmlRegisterType(QEQRParser, 'org.electrum', 1, 0, 'QRParser')
         qmlRegisterType(QEFX, 'org.electrum', 1, 0, 'FX')