Code cleanup proposal

[rotdrop]

Hi,

I have looked through the code and have some code cleanup proposals:

• switch to the more modern Application class instead of using the old appinfo/app.php. #92
• re-enable the CSRF check. Were there reasons for disabling?. #93
• WIP: modularize the code a bit and try to use less of the internal APIs in favour of public ones. #91

91 also has a fix for removing black-listed files, NC would otherwise refuse to delete the extracted directory tree.