* compiler: Add propgrid to the compiler flags dialog (don't allow modification/deletion of categories)
* compiler: Add propgrid to the compiler flags dialog (pre-select the category in the flag editor dialog)
* compiler: Add propgrid to the compiler flags dialog (sort flags in each category)
* compiler: Add propgrid to the compiler flags dialog (make sure that "General" is added first)
* compiler: Add propgrid to the compiler flags dialog (add expand/collapse all popup menu options)
* compiler: Extract some flags from the warnings category to the general category in the common-warnings file