Also some minor refactoring.
This feature works with mp3 right now - may work on other formats, but that will be a seperate commit.
It is not enabled so most of the changes won't even be compiled, and those that do won't be run.
To enable it uncommment the EXPERIMENTAL_ODFFMPEG def in Experimental.h
* /ExtendedImport/OverrideExtendedImportByOpenFileDialogChoice preference enables the override (backward-compatibel behaviour), and it is now false by default
* File names (and mime types) and patterns are Lower()'ed before being fed to wxMatchWild(), now matching should be case-insensitive
* Now empty rule elements (empty list of extensions, empty list of mime types) will match anything (just as if they had one "*" element)
* "Extended Import" preferences tab is now next to "Import/Export" tab
* Preferences now use Grid class (the one used in Tag editor) instead of default wxGrid. Tabbing now works correctly.
* First attempt to add Drag'n'Drop re-ordering for Rule table. Seems to be working.
* Cleaned up a couple of cruft code comments.
* Separate buttons (with hotkeys) for moving rules and filters up and down (ctrl+up/down still works)
* Moved some code into helper funcions (can be called from both button and keyboard event handlers)
* Grid is now configured in PopulateOrExchange (the same way it is in Tags.cpp)
* Keep selection while moving table rows and list items
* Detect trailing/leading spaces in rule condition and offer to trim them
