* qt/accessibility.cpp, qt/accessibility.h: New.
* qt/Makefile.am (pinentry_qt_SOURCES): Add new files.
* qt/main.cpp (qt_cmd_handler): Use new Accessibility helpers.
* qt/pinentryconfirm.cpp (PinentryConfirm::PinentryConfirm): Use new
Accessibility helpers.
* qt/pinentrydialog.cpp (PinEntryDialog::setDescription,
PinEntryDialog::setError, PinEntryDialog::setOkText,
PinEntryDialog::setCancelText, PinEntryDialog::setQualityBar,
PinEntryDialog::setGenpinLabel, PinEntryDialog::setCapsLockHint,
PinEntryDialog::setConstraintsOptions): Use new Accessibility helpers.
(PinEntryDialog::textChanged, PinEntryDialog::checkCapsLock): Guard
code using accessibility features with #ifndef QT_NO_ACCESSIBILITY.