Since the window borders are unknown for a short time after window creation on
Linux, restoreWindowStateFromString() needs to adjust the restored position
before passing it on to the XWindow system.

The adjustment is dependent on whether we use the native or the JUCE titlebar.
Hence the adjustment can only be correct if the titlebar configuration has
already happened before calling restoreWindowStateFromString().

This commit removes the various compiler-specific JUCE_DEPRECATED macros and replaces them with C++14's deprecated attribute. It also removes the JUCE_CATCH_DEPRECATED_CODE_MISUSE flag as we can rely on the override specifier catching usage of these old virtual methods, and tidies up the DOXYGEN preprocessor checks as they were inconsistent across the codebase.

Without the BOM, VS assumes UTF-8 strings (subproject file names etc.)
are ansi-encoded.

- Add AlertWindow::show() and showAsync() methods that take a MessageBoxOptions argument
  - Add NativeMessageBox::show() and showAsync() methods that take a MessageBoxOptions argument
  - Update the DialogsDemo to demonstrate the new methods
  - Deprecate AlertWindow::showNativeDialogBox() in favour of the NativeMessageBox methods
  - Pass button strings specified in MesssageBoxOptions to native dialog boxes correctly
  - Use modern TaskDialog on Windows for the native dialog box where available

See BREAKING-CHANGES.txt for more details.