Transaction hashes can now be copied to clipboard

In the transaction detail activity, clicking on the transaction hash now copies
it to the clipboard and displays a toast in the convention of other 'copied to
clipboard' toasts in the package
deny to load encrypted wallets from the future
throttle view updates even more aggressively
show file creation date in import keys dialog
allow importing keys from automatic backups to internal storage
show security of exported key files in import dialog