differentiate delete from close icon
use consistent icon for 'restore'/versions/history, also SVG
transparent background for lock icon
use mail icon consistent with Mail app icon
remove unused big images
remove unused loading spinners, just have one
use proper style for add icon
standardize on 32px loading spinner, decrease size in CSS where needed
use history icon in Deleted Files template as well
Implement X-Sendfile2 for resume support in LigHTTPd

LigHTTPd does not support HTTP Range headers with the X-Sendfile header in the way Apache does. Instead, it needs to be handled in the backend. This commit does exactly that, using the X-Sendfile2 header to send ranges of files.
To accomplish this without breaking web servers that don't support X-Sendfile2, a new variable MOD_X_SENDFILE2_ENABLED was introduced to separate this method from X-Sendfile and X-Accel-Redirect.
Update files.php
Revert most changes for testing
Reviewed code for X-Sendfile2

Made some small changes which might have caused a segfault on ci.tmit.eu earlier.
Optimize pictures with optipng and scour
Fix lazy styles loading in IE8
Fallback to border instead of box-shadow
change delete from entry forbidden sign to proper icon
handle anonymous upload to reshared folder
fixing Notice: Undefined index: isPublic
fix insertIfNotExist return value, update doc and corresponding test