Added sorting by name, date or size ascending/descending

Hello,
I have added the possibility to sort files/folders by name, date or size.
The option is stored temporary, so it is obeyed if the directory is changed.

Filename sorting fixes also #379 
Sorting by size: Folder are sorted by name, as there is no information about the number of files containing the directory.

Sorting is, like dolphin or windows explorer, separated between folder and files.

TODO: Translate to other languages.
This file was entirely copied. I think it would be better placed in other part so that it's clear that it's being reused.

For the moment, move it to a new folder named something like src/third_parties/DaveKoeller/ ; place with it also a copy of the GPL license, version 2.1.

We have to think a bit how to place this & the external jars , and match it all with the update to Gradle build.