fix #23: jumping depth slider on mouse wheel

This targets bug report #23. With a modified wheelEvent handler the
depth slider can be adjusted in single steps when turning the mouse
wheel.

In my opinion it is also more natural to have something that controls
depth from high to low to be arranged in vertical direction.
fix for #15: adding keyboard control to depth (Y)

Added keyboard control for depth (Y) slider. When MapView widget is
selected (e.g. after moving zooming) there are now keys to
increase/decrase depth level: HOME END + -
While holding down SHIFT it is also possible to use the mouse wheel to
change depth instead of zoom.
simplified depth control with mouse wheel

Previos code was too complicated, as SHIFT status is already present in
wheelEvent.
Merge remote-tracking branch 'upstream/master' into ControllingTheDepthSlider
fixes to block IDs

large flowers are defined only by bottom part -> made top part
completely transparent
fixed id numbers for new door types
moved alpha definition up

There might be a problem with variant blocks not getting the correct
alpha value if the json file is parsed top to down. Therefore it is
better to define all values to be inheritted by the variants before
defining the variants itself.
fixed depth shading

There was a bug in depth shading with semi transparent blocks on top.
With the new blending Flowers and other alpha<1.0 stuff doesn't pop out
anymore.
Support for viewing/browsing entities on the map
Merge pull request #45 from thewierdnut/int

Support for viewing/browsing entities on the map
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master' into ControllingTheDepthSlider
added configuration for vertical/horizontal depth slider

Now the setting dialog box contains a checkbox to select if the
traditional horizontal depth slider shall be used or the new proposed
vertical one.
I decided that the change will take place only after a Minutor restart,
as it would be complicated to change the layout after setup.
The setting dialog is also converted to a Qt Form, which makes it easier
to add changes.
Merge pull request #40 from EtlamGit/ControllingTheDepthSlider

Controlling the depth slider with mouse wheel and keyboard
Fix for entity rendering X error

The pull request from thewierdnut renderes entities at a X position one
towards west. With this change entities are rendered at correct X
position (at least in my tests).
added id for Piston Extension

ID 34 is the head of a Piston and ID 36 is a technical block describing
all the stuff moved by the Piston. But Í have no idea about a good
color.
Merge pull request #47 from EtlamGit/master

block ID fixes + entity rendering fix + depth shading fix
Fixed tabs
Add in support for generated structures and map overlay

* fixed coordinate offset
* moved entities to overlay
* different entity types have different colors
* generated structure properties can be browsed by double clicking on the map
Fix whitespace
Entity properties work for horses again