Introduced a minimap

This is a quite stable running navigator or minimap.

With the help of MapRenderer a small version of the map is rendered into
a buffer image. The minimap rendering is copied from the screenshot
function and offers several flags to finetune the rendering.

For detecting mapchanges I used the indexChanged-event offered by
QUndoGroup. That does a pretty good job. Minimap rendering can be
expensive as it has to draw the entire map. To prevent slowdowns during
painting an (optional) timer is used that drops all redraw calls until
100ms are elapsed.

The overall performance impact seems to be okay. At least on my machine
(win7 64bit, quadcore i7 with good graphics card). This certainly needs
to be tested in different environments.
Fixed some compiler warnings

Unused variable and initialization order warnings.
Coding style fixes
Remove special directories for moc, ui, rcc output and objects

Not specifying special directories for these files simplifies the needed
parameters to `cppcheck`.

If the build directory is supposed to stay clean, a shadow build should
be done.
Fixed include style for math.h

Noticed since using 'local first' include style makes `cppcheck` complain
about not being able to find the file.
Silence a bunch of cppcheck warnings

This includes one actual bugfix: the missing initialization of
LuaTableWriter::m_suppressNewlines.
Added static code analysis to the .travis.yml file
Flareplugin: fix objects layer, if layer already exists.
Removed option that is not available yet in cppcheck 1.52
Avoid crashing on roaming scroll bar pointers

Happened after closing the last map and then opening a new one.
Bumped version to 0.9.0 and updated NEWS file

This is not the release yet, but it is an attempt at signalling a soft
feature freeze so that we may start polishing for release.
Fixed some issues with the minimap

* Corrected small issues with updating the mouse cursor.
* Use the background color specified by the map and otherwise default to
  the same color used by the MapScene.
* Do delayed repaint of the image also on resize events and when switching
  maps, for performance reasons.
* Fixed pixel rounding glitches in viewport indicator rectangle.
* Specify a minimum size of 50x50 pixels.
* Implemented sizeHint() to return 200x200 to get a decent default size.
Fixed crash when trying to capture terrain from an empty area
Renamed Navigator to Mini-map
Don't install libtiled header files by default

Installing the header files breaks our current Debian/Ubuntu packages.
Since there is no real need for the headers to be installed, it has been
made optional and disabled by default.
Some small optimizations

Seems not to be having much effect, though.
Optimized updating of the Tilesets dock

When switching maps the Tilesets dock was doing a lot of work, which
became noticeable with maps carrying dozens of tilesets. Two things were
done to make it fast again:

* The dock widget is temporarily hidden while it is being updated, saving
  a lot of time that was being spent needlessly relayouting the tab bar.

* The tileset models are being created on-demand, when the user actually
  switches to a certain tileset.

Now even maps with over 50 tilesets perform reasonable. If needed, it
could be further optimized by also creating the tileset views on-demand.
Fixed crash when zooming tilesets or toggling the tileset grid

Two places in TilesetView were not yet taking into account that the
tileset model is being created lazily now.
Update .mailmap file
Updated Alex Vega's name

On his request.