ux: make show file after/before links unclickable and black if they are disabled

diffs: replace compare controller with new html based diffs: * side/side + unified support * redesign of diff changes/operations * added button to see file before the change * auto collapses large diffs refs #4232

files: don't load the file if it is over the size limit since it won't be displayed anyway - increases speed of loading the page when a file is too big

nix: add pygments-markdown-lexer for highglighting markdown files

system-info: expose inode limits and usage. Fixes #4282

packaging: bumped psutil to latest version

codeblocks: add new code token rendering function that supports diff and normal tokens.

svn-support: Only add reload-cmd subscriber if a reload command is set. If no reload command is set in the ini file there is no need to add the subscriber to the event.

svn-support: Add missing argument to tmplate context. This argument was only added in the view handling GET requests. But in case of an error the POST view also rederes the template and threfore need this arguement.

svn-support: Only show 'generate config' button if config generation is enabled.