Update pgmagick requirement for Mac OS

Installation failed on Mac OS with pgmagick 0.5.5 (libboost library
could not be found because of an error in the install script). This was
fixed in 0.5.7
(https://bitbucket.org/hhatto/pgmagick/commits/977a2d1862553198d347464bb
7ca2ea7efcf6090)
Add ProjectStackInline to ProjectAdmin

ProjectAdmin now shows associated Stacks. Also renamed ProjectInline to
ProjectStackInline to better reflect the model name.
Merge remote branch 'felix/small-fixes'
Fix problems with overlays in stack window

If the slider for an overlay is set to 0 (i.e. smaller than 0.02 to
be precise) - the tilelayer is removed from the DOM and kept only
as a reference. Tiles are then not fetched. In the Django admin
interface, set the default opacity to 1 (or a value in the range 0
to 100) to isolate the tile layer by default when loading the stack.
This allows now to have many overlays attached to a stack, but only
fetch the tiles for the overlay you turned up the opacity value.
To avoid confusion, rename OverviewLayer to TilelayerControl.

Readd the instantiation of the OverviewLayer only for the 'TileLayer'
layer, not for overlay layers, to enable fetching of the small thumbnail
images in the bottom-right map.
Forgotten renaming of tilelayercontrol
The path format for overview maps now depends on the tile source type.
For type 5, the path is now <baseURL>/small/<layer>.<ext> .
Merge pull request #549 from perlman/master

Source-type dependent paths to overview (mini) images.
Fix NetworkML export by adding characters in front of numbers
when assigning these to any "name" attribute.
Otherwise, neuroConstruct fails to import.
NetworkML export: include the neuron's name.
Webglapp: enable changing the color of the mesh(es) in the options dialog.
While at it, properly repaint the mesh when loading it, and remove unused code.
Clustering: Add toolbar button to create clustering window
Clustering: Add basic clustering front- and back-end
Clustering: allow sub-path as features

When selecting the "Use sub-paths as features" option, all sub-paths
starting at the root on a way to a leaf will be added as features, too.
This means a path doesn't need to end with an ontology defined leaf, but
it can also end in the middle to be respected by the clustering.
Clustering: use SciPy to do the actual clustering
Add gRaphael line graph v0.5.1 library
Add world/screen coordinate translation methot to gRaphael line chart
Add min/max axis options to gRaphael line chart
Clustering: draw a basic dendrogram
Clustering: show cluster names when hovering the dendrogram