Better error handling on non-expected response on overview page
FIX: maps now to be shown in list are again hidden in lists
ajax.js: Don't set content-length or connection headers for XHRs

These headers are removed, and set by the browser for security reasons
[1]. These lines showed up as errors in Chrome's error console.

  1: http://www.w3.org/TR/XMLHttpRequest/#the-setrequestheader()-method

Signed-off-by: Carl Helmertz <chelmertz@op5.com>
Signed-off-by: Lars Michelsen <lm@larsmichelsen.com>
FIX: Ajax request: Not setting headers which are usually set by the browser