Major update

* Added Quick Look and Open In to file actions menu
* Added option to open a folder in Shellista (most forks work)
* Added dynamic thumbnail icons for images (doesn't work with certain PNG files for unknown reasons)
* Finished flag analysis for files and folders
* Made external access easier, created a ShellistaExt plugin
* Started work on caching file properies to improve efficiency, not yet fully implemented
* Various minor additions, optimizations and fixes