Open/Save dialogs - configurable filters #258

Currently both dialogs display All files (*.*). I have checked the code and it seems this is hardcoded, isn't it?

Need to make this string customizable:

• read the value from the INI (e.g. as a string of form Caption|*ma.sk|Caption 2|...) instead of the hardcoded All files (*.*)
• the default value for that option is the current All files (*.*) (Notepad2 behaviour)
• when an Open or Save dialog is submitted - remember the selected filter
• when displaying an Open or Save dialog restore previously used filter (if there was none then the first)
• no need to save last used filter to settings (when starting the process default to the first filter)