* add missing support for ofFileMustExist, by default enabled in TExtFileOpenDialog
* store and restore previously selected path
* support single FileName when MultiSelect is true
* avoid setting unwanted tree path when caller provides an empty FileName or InitialDir
* set different default form caption for open + save mode (todo: include lclstrconsts translation files in packages)
Refs #2268
* TOpenDialog => TExtFileOpenDialog
* TSaveDialog => TExtFileSaveDialog
* show encodings and linebreaks only when the caller sets data for these
* show selected path from tree in label at top
* support DefaultExt string
* support OnTypeChange event
* disallow changing tree folder for ofNoChangeDir
* catch EInvalidPath in SetInitialDir
* show hidden folders in tree
* enable sorting in file listing
Refs #2268
