Add interfaces::ExternalSigner to let signer objects be passed between
processes and signer code to run in the original process, without
multiple processes linking and running signer code.
When no external signers are available, the option to enable external
signers should always be disabled. However the encrypt wallet checkbox
can erroneously re-enable the external signer checkbox. To avoid this,
CreateWalletDialog now stores whether signers were available during
setSigners so that future calls to external_signer_checkbox->setEnabled
can account for whether signers are available.
This commit makes it so that when the `Blank Wallet` checkbox is auto-selected after the user selects 'Disable Private' keys, unselecting it will also unselect the 'Disable Private Keys' checkbox, which in turn re-enables the 'Encrypt Wallet' checkbox.
ac7ccd67d7f2b09e36dd57405f899e4698dd3d78 scripted-diff: Remove unused "What's This" button in dialogs on Windows (Hennadii Stepanov)
b6951483ecdd4409a0e1d492c93bcd4d823f039d qt: Add flags to prevent a "What's This" button on Windows OS (Hennadii Stepanov)
Pull request description:
Fix#74.
From [Qt docs](https://doc.qt.io/qt-5/qdialog.html#QDialog):
> The widget flags _f_ are passed on to the `QWidget` constructor. If, for example, you don't want a **What's This** button in the title bar of the dialog, pass `Qt::WindowTitleHint | Qt::WindowSystemMenuHint` in _f_.
Screenshot on Windows 10 (2004):
- master (3ba25e3bdde3464eed5d2743d68546e48b005544)

- this PR (e322fe7e19ac504272d14b9b4f9b28b13df888ed)

ACKs for top commit:
Bosch-0:
tACK ac7ccd67d7f2b09e36dd57405f899e4698dd3d78 Tested on Windows 10.0.18363 Build 18363.
promag:
Code review ACK ac7ccd67d7f2b09e36dd57405f899e4698dd3d78 but with some suggestions.
jonasschnelli:
utACK ac7ccd67d7f2b09e36dd57405f899e4698dd3d78
Tree-SHA512: f6750a17b7203106cb4db5870becba1cef6a505d4edcc710ba131338bd3aae051510627e62c9bcb8345a7f497c614709e11aeb8f6ae3ea85967bbce2a8c69e64