Set minimum widths for the columns of the hotkeys editor on OS X

The OS X implementation makes very poor choices for the default widths
if given the opportunity.
Fix issues with selected line styles with the keyboard on OS X

Opening the style list dropdown and switching between values with the
arrow keys doesn't update the value returned from ctrl->GetValue() on
OS X, but the event contains the correct value so use that instread.
Add #ifdef __cplusplus to the precompiled headers to make Xcode happy
Delete osx-run.sh

wxWidgets now supports running from outside application bundles, so it's
no longer needed.