Revert "Only fetch tiles when opacity bigger than 0. This speeds up fetching from multiple HDF5 tile sources such as with many overlays"

This reverts commit 336ba450b57b94014424a084cad636b9d0b7739f.
No need to copy twice
Add X-Requested-With header for request send with request queue

According to [1] the 'X-Requested-With' header is used to identify AJAX
requests. If it is an AJAX call, the header field's content should be
'XMLHttpRequest'. When the request queue is used to create a request,
an AJAX request is issued. Therefore it should be marked as such.

Django's request.is_ajax() method checks this header field and returns
true if it is present and its value is 'XMLHttpRequest' [2].

[1] http://en.wikipedia.org/wiki/X-Requested-With#Requested-With
[2] https://docs.djangoproject.com/en/1.4/ref/request-response/#django.http.HttpRequest.is_ajax
Add visualization for labels in 3d viewer
Merge remote-tracking branch 'origin/master'
Cropping tool: fix response status code handling bug
Merge branch 'feature/ontology-editor' into config-eaton-features
Add thumbnailing tool for cropping one slice and saving the URL to its view
Add adjustable composite tile layer

This commit adds a an "Adjustable composite" link below all the stacks of a
project. This link allows to create on-the-fly tiles based ot the intensity
settings in the GUI. There, sliders allow to adjust the intensity of each
stack in the project. Dapending on the stack(s) this could involve quite
some memory and CPU requirements. The server configuration might be
tweaked to cope with that.
Thumbnailing tool: allow to export multiple stacks and default to 'all'
Thumbnailing tool: add marker creation functionality
Cropping tool: use microns as output unit
Add a link to the internal Redmine instance to the front page
Add notes and links to an english and a german imprint
Adjustable composite: add job class and separate processing function
Add gevent WSGI server run script
Support thresholds for adjustable composite display
Thumbnail tool: add testis folder
Adjustable composite: allow maximum intensity of 1000%
Import script: allow recursion into sub directories